In the year 1975, a five-year-old girl is dropped off at an orphanage by the family that adopted her. The nun in charge tells her there will be another family that will connect with her. Flash forward to 1980. A now ten-year-old girl (played by Melissa McCarthy's oldest daughter) is dropped off by her recent adopted family; she asks why nobody wants her. The nun still inspires hope. Now, in 1985, the young girl is now a teenager. She is dropped off by her adopted family and tells them "Fuck you", flipping them off as they drive away. The nun tries to give encouragement but the teenaged girl tells her she doesn't need anybody in her life; she is fine being alone.
It is now present day. An amphitheater is filled to the brim with fans of Michelle Darnell (Melissa McCarthy), all grown up. She is lowered from the stage on a mechanical phoenix and begins to do a (rather impressive) hip-hop dance number with T-Pain and shirtless male dancers. She then talks to the audience, referencing her many self-help books on how to get rich and tells the crowd that if they have family in their life, they should just push them away because they just hold you back. She also points out that she is 47th richest woman in the world despite not having a family.
Michelle goes up to the rooftop of the building with her assistant, Claire (Kristen Bell), to board a helicopter from a helipad. A man is waiting with an envelope. Inside is a cell phone; it rings, revealing a photo of a samurai. She knows its her rival, Renault (Peter Dinklage) who likes to think of himself as a samurai; Michelle notes that when she first met him, he was Reynold. He is standing on a nearby rooftop with his goons. He taunts Michelle and then asks how she was able to make such a good stock deal. She tells him its insider trading and he needs to get in on it. Claire gives Michelle some last minute notes about her week and then Michelle flies off, flipping off Renault from inside the helicopter.
Michelle gets back to her estate in Chicago and goes into her gigantic office with her security guard, Tito, and Claire. Its time for her teeth whitening so she puts the cheek and lip retractor in her mouth and has a long conversation while wearing it. Claire points out that exactly one year ago that day, Michelle told her she would give her a raise; she even reads the quote out loud as she had written it down. Michelle teases Claire, with Tito siding with her, before Claire says that if she doesn't get a raise after being such a good assistant on call 24 hours despite being a single mother, she will quit. Michelle pretends to be astonished that she has a kid but ultimately says she is teasing and that she will give Claire a raise. She wanted to see some aggressiveness in Claire and is impressed. She gives her a pair of earrings that cost her $62,000 in 2001; she said that will count as her raise. Claire accepts.
On her show, Gayle King interviews Michelle about her new book but begins to bring up her past, particularly how she was an orphan and raised by nuns. Michelle claimed it was a magical experience, like growing up in Hogwarts, but Gayle shows a picture of her as a teenager looking miserable in front of the orphanage. Gayle then shows Michelle a video of a former mentor (Kathy Bates) who complains about Michelle's attitude, calling her a B-I-T-C-U-Next-Tuesday. Michelle voices anger at being ambushed and storms off, telling Gayle its stupid to spell her name with a Y. When she goes outside, the police are there and they arrest her for insider trading. Even though she claims everybody does it and refuses to go in the car (straddling her legs against the door frame), she eventually is taken in and does jail time.
Michelle actually has a great time in jail. On the tennis court, her lawyer (a cameo by the director and Melissa's husband, Ben Falcone) tells her all her assets and properties have been seized. She hits a tennis ball at his throat and tells him she's going to find another lawyer; he calls her a stupid ginger. She says, unlike others, she's a genuine redhead but hell never know firsthand if her curtains match the drapes because shell never sleep with him (a inside joke because, in real life, he's the father of her children).
Four months later, Michelle is released from jail. All of the inmates say goodbye to her and a prison guard even comes on her day off to say goodbye to Michelle. The gates open and nobody is there. Michelle says she assumed a car would be waiting for her which makes the prison staff laugh.
Michelle takes a taxi to her home but it has a foreclosure sign on the gate. She instead ventures over to the small apartment of Claire's, above a bodega. She buzzes and a young girl sticks her head out the window above, telling Michelle that Claire isn't home. She also tells Michelle she knows who she is a convicted felon. Michelle chastises her for saying it so loudly and tells passersby that it was a white collar crime. Claire's daughter finally explains that Claire is at work.
We now see Claire at her new job. As she settles into her cubicle, her boss (Cecily Strong) chastises her for being three minutes late. Claire's coworker, a laid back guy named Mike (Tyler Labine), tells their boss that everyone downstairs is gushing about how much they love her and Claire was late because she was part of the conversation. The boss leaves to eavesdrop and Claire thanks Mike for helping her. He asks her out on a date but she politely refuses.
When Claire arrives home, she sees Michelle waiting for her downstairs. She takes her into her home and gives her a single box of items, telling her the rest of her property was seized. Michelle cant believe it. She expects Claire to still be her assistant but Claire says shes found another job in the four months Michelle's been away as did Tito, who changed his sycophantic tune after Michelle's arrest. Claire suggests Michelle stay with a friend but realizes Michelle doesn't have any. Even though her daughter, Rachel, originally was dismissive to Michelle, she convinces her mom to let Michelle stay there as opposed to being turned out on the streets.
Claire sets Michelle up with a sofa bed, which she cites as being comfortable. After she walks away, Michelle admonishes the idea of a bed built into a sofa (having only lived with the finest of things) but says she finds it comfortable. Just then, the bed retracts, shooting her violently into the wall (a really funny sight gag). Cut to Claire asleep in her bed; she wakes up to find Michelle laying next to her. Michelle explains that the bed threw her against the wall and that she went into the kitchen and enjoyed the Doritos she found, a snack she apparently had never heard of before.
The next morning, Michelle uses self-tanner on herself in the bathroom despite Claire warning her that it dries darker and will make her orange. She bends over in her robe to ask about streaks which terrifies Rachel, who passes by at that moment.
Now the CEO of a successful company, Renault explains to his henchman why he hates Michelle so much; years ago, they used to date. In a flashback, we see them making out in the copy room while their colleague, Bryce (Michael McDonald), tells them to come to the main office because they're going to announce who gets the promotion. Renault is sure it will be him but its actually Michelle, who whispers to him that she stole his client list so that she could claim the promotion for herself. All this aside, their relationship was authentic because they both comment throughout the film about how attractive they found the other back in the day.
In present day, Michelle is bound to get back on her feet as a businesswoman. She goes to a country club and some of her former colleagues, including Bryce, are chatting at an outdoor table. They are all rude and dismissive to her so she insults them all brazenly, telling Bryce that his deceased wife had sex with all the IT guys at the company and is now doing the same in Hell. After Michelle walks away, she falls down a flight of concrete stairs. Her former colleagues gather at the edge and comment that they're surprised she survived. Renault's henchman has videotaped the whole thing on his phone and shows it to Renault in a limo. He notes that hes glad that the colleagues he hired were rude to her, as he paid them to be.
Michelle recovers from her fall at home while Claire is at work, complaining that everyone embraced Martha Stewart after her prison sentence. Rachel takes care of Michelle by bringing her food. She is in love with the brownies that shes told were made by Claire at home. When Claire returns from work, Michelle volunteers to take Rachel to her Dandelions meeting on her behalf. They arrive at the school with a meeting in session. The leader (Kristen Schaal) is telling everyone that her cat, Spaghetti, is doing much better after being ill. The woman next to Michelle gushes on and on about how much she loves Spaghetti and Michelle gets weirded out. When they move on to the topic of cookies and the thousands of dollars they made from cookie sales, Michelle realizes she can make money through baked goods sales. She tries to encourage the crowd of this but a mother named Helen (Annie Mumolo, co-writer of Bridesmaids) points out that Michelle shouldn't be there because shes a felon. Michelle addresses the crowd but constantly whispers nasty things to Helen, telling her shes going to fuck her up.
In the middle of the night, Michelle wakes Claire up to pitch an idea to sell the brownies Claire makes so well. Rachel wakes up and joins them in the living room. Michelle chastises Dandelions and says they make tons of money and all the girls get are stupid badges. Claire tells her its a non-profit organization and that it has value for girls. Rachel is prompted to explain she got a badge for starting a conversation with a stranger for 30 minutes and being a good hostess. This leads Michelle to point out the Dandelions is anti-feminist and if Claire supports it, the logo should be a woman wearing an apron, bent over in the kitchen because shes giving a blowjob to a man. Michelle says, if Claire makes brownies for her to sell, they will be 50/50 business partners, and a part of the profits will go to the young girls selling them so they can earn money, too. Claire says shes not going to quit her job; starting a business is too risky. Michelle tells her she can remain an employee and just make the brownies on the side, pointing out that if they create revenue, Michelle will move out. This is all Claire needs to hear to get her on board.
At school the next day, Michelle sits with Rachel and scopes out possible recruits for their brownie business. They select a really tall girl amongst some other tough kids. Rachel is excited that Michelle is letting her drink coffee. As shes about to head out to school, knowing she has to approach girls about joining their team, she admits to feeling sluggish and dizzy. Michelle notices she got their coffees mixed up and hers had bourbon in it.
At the next Dandelions meeting, the leader is giving a speech about how Spaghetti has died. Michelle and Claire interrupt, pitching their idea to sell brownies and asking the young girls to join. Michelle tells the girl they'll get five percent of profits but Claire points out they agreed to ten, much to Michelle's chagrin. Helen defends the Dandelions but Michelle points out the organization does stupid things like building nests for small animals which the leader admits is what they're scheduled to do next. She tells the girls they can make actual money to put towards college so they don't have to be a stripper and also hints that Helen's daughter is going to be a lesbian when she grows up. Michelle leaves her brownies to entice people to join; a handful of mothers and daughters follow behind. Helen tries the brownies and goes gaga over how good they are.
After forming a team, the girls begin to sell the brownies successfully going door to door, as well as targeting places like marijuana dispensaries. As promised, Michelle gives out a portion of the profits to the girls. When they get to a wealthy neighborhood, Michelle tells them they can charge 20 dollars a box because rich people will be skeptical of any brownie that is inexpensive. Helen and the Dandelions appear and tell Michelle that shes infringing on their turf. The two bicker back and forth, escalating into Helen punching Michelle. Michelle punches back, harder, and then all the girls and mothers begin a huge, disturbingly violent street fight.... filmed in slow-motion. In the end, the street is on fire as are some of the Dandelions cookies which Michelle comments as, That batch is burnt.
Michelle visits Claire at work and tells her she needs to come home because they've run out of brownies. Claire reminds Michelle that she was told she could have both jobs but Michelle points out that shes working in a tiny cubicle and it seems like a horrible gig. Claire's boss returns and gushes over Michelle, whom she is a fan of. Mike tries to encourage Claire to do whats best for her and reminds her of the pity date she almost agreed to. Michelle tells him he should embrace the pity because its the only kind of date he can get. Claire finally quits and subsequently asks Mike out to dinner.
Claire gets ready for the date and Michelle and her have a long debate about the sweater she's wearing and the fact that she's in a nursing bra because she finds it comfortable. Michelle plays with the straps and then lifts up Claire's boobs, showing her where a normal bra would have her boobs land. Claire asks Michelle if she would like if her boobs were fondled and both begin pawing at each other. Rachel enters and they try to play the moment off. The debate ends as Rachel tells her mom not to wear the sweater.
Mike comes to the apartment to pick Claire up. Michelle stays behind to babysit, joking that she and Rachel are going to watch The Texas Chainsaw Massacre while shes gone. Mike and Claire have a nice date in a restaurant. She doesn't usually have a baby-sitter so shes glad she could trust Michelle. Cut to them back at home with Rachel covering her eyes while Michelle watches The Texas Chainsaw Massacre, commenting that its the best part, where a girl gets cut up with a chainsaw (although the footage is actually the end of the movie when the character escapes).
With the brownie business booming, Michelle visits her mentor on her large estate, to discuss an investment. Even though Kathy had called her a C-U-Next-Tuesday on television, she now admits that she likes that about Michelle and agrees to help a female in business. Michelle, Rachel, and Claire go to a nice sushi restaurant to celebrate their financial success. Michelle arranges for a pizza to be delivered to Rachel since she doesn't like sushi. She herself orders a puffer fish which she says is dangerous because if its not prepared properly, it could paralyze her. As she talks, her mouth goes numb which worries Claire. Then Michelle goes completely limp for a full ten seconds, falling backwards in her chair and moaning, before recovering. She says that going to the brink of paralysis means its good puffer fish. Rachel surprises Michelle with a hand-painted frame she made in school with a photo of the three of them inside, commenting that they're like a family. At the mention of being a part of a familial unit, Michelle gets uncomfortable and leaves, telling them that she'll pay the bill on the way out.
The next day, Claire has to pick up Rachel at school because Michelle is a no show, despite Rachel claiming she texted her 50,000 times. When Rachel and Claire get home, there is a note from Michelle saying she thanks them for letting them stay there and hopes they get a new couch that isn't so dangerous. Claire points out how impersonal the letter is despite bonding over the last few months.
In a private jet, Renault has his henchman serve him one of Claire's brownies, as well as pour milk into his mouth from a goblet. Renault loves them and decides he wants to take over the enterprise, citing that hes even willing to try to hold the glass of milk himself to drink, which he does.
Time has passed and Claire and Rachel make their way to a venue, complaining that Michelle has been so distant, Claire wasn't even pre-warned about the press event that Michelle has scheduled. Outside the building, Renault is waiting in a limo; he stops Claire to ask her if she wants to sell the business to him. Michelle watches this exchange from inside the building, not able to hear their conversation. When Claire arrives, Michelle is distant. She tells the barrage of camera crews that she has opened the new facility with state of the art technology to make mass batches of the company, eliminating Claire's involvement as a baker. Claire pulls her aside, complaining that she's a 50/50 partner and these decisions have to be discussed with her. Michelle responds coldly, claiming she was doing something nice but it went unappreciated. She storms out of the building, telling Claire she doesn't want to see her or her daughter ever again. Rachel begins to cry.
Michelle gets drunk and walks around Chicago, feeling guilty. She goes to Renault's office and presents a deal to him. Back at Claire's apartment, Rachel calls Michelle an asshole. At her home, Michelle drinks wine at a giant table alone and then calls herself an asshole. She finally takes down the giant painting she has hanging on the wall and replaces it with the tiny framed photo of her, Claire, and Rachel.
Mike and Claire are now dating and he is over at her house late at night. Rachel opens a closet door and screams "Holy shit!!!!!". Claire runs over and says the same thing. Reveal Michelle hiding in the closet. She explains she didn't want to wake them so thought shed just come get her things when no one was up and then heard them so she ended up in the closet. She tearfully apologizes for her behavior and explains she always avoided being in a family after being abandoned in her youth and that it was wrong of her to react so poorly to being a part of one now. Claire forgives her. But Michelle tells her she sold the company to Renault, citing that she saw Claire and Renault talking about doing the same thing. Claire tells Michelle their conversation regarded Claire telling Renault she didn't want to sell. Acknowledging the misunderstanding, Michelle realizes she signed the contract on Friday night and Renault wont show it to anyone until Monday, which is the following morning. If they sneak into his office and claim it, no one will know the deal was ever made. Claire points out that he probably scanned it and emailed it to lawyers immediately after receiving it but Michelle points out that hes afraid of doing anything digitally because he has a fear of being hacked.
Late at night, Mike, Claire, and Michelle go to Renault's office building to break in and steal back the contract. As they approach, Claire tells Michelle not to bring any guns but Michelle is adamant she hasn't. When Mike applauds her, citing that he looked it up and there is minimum jail time if they are unarmed but a massive sentence if they harbor a weapon, Michelle reveals a handgun which she promptly throws in the garbage. She goes over the plan and we see it in action as she explains Claire and Michelle will run up the stairs, with Michelle doing all kinds of gymnastics in the sequence, while Mike will stall the security guard by sucking his dick. This confuses Claire and Mike, who asks why he has to suck anyone's dick. Michelle tells him she's the brains of the operations and Claire doesn't want to; Mike tells her he doesn't want to. They have a long debate about whether or not he should suck someones dick before Michelle nixes the plan, complaining it took her a long time to figure it out.
When they get to the top floor, they cant enter the building because its locked. Luckily, Michelle swiped the guards key card. They admire a statue in the lobby and note Renault's taste for samurai memorabilia. Michelle comments he once killed someone in Puerto Rico with a samurai sword. They raid his office but cant find the contract. They are startled by someone approaching but it turns out to be Mike. They then find the contract in a folder in Renault's desk. However, Renault is actually on site, finishing up a Skype conference call with businessmen in Japan. He walks in on them escaping with the contract. Claire interrupts to tell him the contract isn't valid because she owns 50 percent of the company and she didn't agree to it; Michelle tells her that the 50/50 thing was a concept that she never got around to putting down contractually. Michelle points out that Renault doesn't even want to own the business. He agrees, that he just wants revenge for Michelle stealing his job years ago. He grabs a katana (samurai sword) off his wall and charges at Michelle with it, reminding her he killed someone in Puerto Rico. Mike shouts out that hell suck his dick. Michelle responds, Not his! and then points out to Claire that he was way to eager to make that offer and shed better be wary. Michelle tries to defend herself against Renault with nunchucks that are in the office but she doesn't really know how to use them and hits herself in the head. She then twirls a bo staff, bragging that she used to be a baton girl and that everyone made fun of her but now she had skills. He slices the bo staff in half. They run away, with Renault and his henchman in pursuit.
The group runs up to the rooftop which makes Claire nervous until Michelle points out that shes been on many helipads. Michelle continues to fight with Renault who finally pushes her off the roof. Claire is then cornered by him and she manages to knock Renault off the roof. Everyone runs to the side to see both Michelle and Renault one floor below, having landed on a soft pile of bags. They reminisce about the time they were a romantic couple and begin to make out, despite Claire's urging Michelle not to. Claire also punches the henchman after he threatens her.
Time has passed and Claire has a housewarming party to celebrate the new home she got with the revenue from the brownie business. Michelle comments that she is glad they've upgraded everything including a new couch to replace the old one. She tells Claire that she actually donated the sofa bed. Cut to Helen, the Dandelions mom, bragging to her daughter that Michelle gave her a couch, which she considers a sign of victory. She lays down on it and, just like Michelle earlier, is flung violently but instead of against a wall, she flies through a window, into the backyard where her daughter is hitting a heavy bag.
During the closing credits, several bloopers and outtakes are featured.