Rather then trusting her witness protection program handler, FBI Agent Victor Machado, sole gangster murder trial witness Bridget Kelly make a run for it on her own, before the trial. She's welcomed in New York by her rich, identical twin sister Siobhan Martin and her dream husband Andrew. Only a suicide note on their yacht informs Bridget that spoiled-rotten Siobhan wasn't happy, but she accepts taking her place as seemingly perfect cover. Shortly after she discovers her twin wasn't faithful either, the whole family is a mess, notably drug-addicted daughter Juliet. ...
FBI Agent Machado tries tenaciously to properly question 'Siobhan', who dodges him as zealously. That game is up when she must organize in one day, with a brilliant gay event planner, a party fro Henry and his partner Olivia's investment firm, and he already decided on the loft where she left the assailant's corpse, which she's now unable to evacuate and must hide. Henry is delighted with the 'old Siobhan' who cares again for him and 'their rebellious junk daughter, not unlike young Bridget. Henry still dodges Gemma's suspicion of adultery and asks 'Siobhan' why they ...
Bridget learns she has a potential clue to bring her closer to Siobhan's killer. Bridget discovers some interesting information about Andrew, which causes tension between them. Meanwhile, Agent Machado continues his pursuit of Bridget and tensions flare between Henry and Gemma over their investment in Andrew's hedge fund.
Still posing as Siobhan, Bridget, and Andrew head to the Hamptons with Gemma and Henry to celebrate her birthday. Despite the close quarters, Henry is dead-set on rekindling his affair with Siobhan. Gemma learns some unsettling news, while FBI agent Victor Machado closes in on some new information, which forces Bridget to reveal some of her past in order to protect her secrets.
Gemma reacts angrily to Bridget's revelation, and threatens to expose Bridget unless she exposes Henry's infidelity. Things get worse from there. Bridget goes to an Narcotics Anonymous meeting and does not give her name. "Siobhan" apologizes to Juliet for "stealing" her dad from her mom, and they begin to reconcile.
When Bridget cannot get in touch with Gemma she begins to wonder if something has happened between Gemma and Henry. Juliet starts a new school, where she defends herself against the school bully and her teacher Mr. Carpenter comes to her rescue. Bridget asks Charlie to do her a favor that could come back to haunt her, while Agent Machado looks into Malcolm's disappearance.
Still posing as Siobhan, Bridget is forced to reveal she has a twin to Andrew and Henry when Agent Machado starts closing in. Henry becomes a suspect in the whereabouts of his wife, Gemma and Juliet starts partying to dangerous extremes. Meanwhile, Malcolm escapes and is on the run from his kidnappers.
Andrew and Bridget are told some upsetting news that also affects Henry. Juliet continues to form an unlikely bond with her teacher Mr. Carpenter and Malcolm shows up in New York, where Agent Machado confronts him. Meanwhile, Siobhan's relationship with Tyler is jeopardized.
Bridget begins to realize she is developing feelings for Andrew, while Henry and Andrew's business partner Olivia bond over common interests. Malcolm is suspicious of Bridget's new NA sponsor Charlie and Bridget makes an appointment with Siobhan's therapist, hoping it will help her discover some insight into her sister's life.
Henry begins to target someone as a suspect in the disappearance of his wife Gemma and realizes he must work with Bridget to find out more information. Malcolm talks to the police about his suspicion of Charlie, while Juliet develops an unhealthy obsession with her teacher Mr. Carpenter. Meanwhile, Agent Machado meets with an informant back in Wyoming.
Bridget offers to host a fundraiser that her friend Greer is holding for Juliet's school and discovers that Greer knew one of Siobhan's deep dark secrets. While back in New York, Siobhan discovers that Bridget has settled into her former life more easily than Siobhan expected and she is determined to change that. Meanwhile, Malcolm decides to work for Andrew at Martin/Charles in order to keep an eye on him, and Henry mourns the death of his wife.
Juliet's mother Catherine arrives in town, where she proceeds to wreak havoc on Andrew and Bridget's relationship. Bridget discovers someone from Siobhan's past and thinks he might be the key to her learning more information about her sister. Meanwhile, Henry discovers a lead that causes Agent Machado to think he is closing in on Bridget.
Bridget visits some of the last locations Siobhan went before she disappeared and discovers that Siobhan kept a secret office. Olivia finds out some information about Henry and blackmails him into introducing her to Gemma's wealthy father Tim Arbogast. Meanwhile, in Paris, Tyler struggles with a moral decision that could affect Siobhan and Andrew.
Bridget encounters Dylan, who was an important part of the sisters' past. After finding something in Henry's possession that belongs to Bridget, Malcolm befriends Henry to keep an eye on him. Catherine asks Andrew to make a big decision regarding Juliet that could change their family dynamic.
Andrew proposes again and Bridget realizes she is in over her head. Olivia becomes increasingly suspicious of Malcolm while he is working at Martin/Charles. Juliet makes a decision that forces her mother Catherine to take drastic measures.
Agent Machado's past with his informant, stripper Shaylene Briggs is revealed and Siobhan deceives Malcolm when she pretends to be Bridget. In Paris, Tyler takes something from Siobhan that is a key piece of evidence in her plot for revenge. Henry realizes Bridget knows more than she should and has to keep her from interfering with his plans.
Bridget fears that something has happened to Malcolm when she cannot get in touch with him. In an effort to find him, Bridget visits the hotel where Malcolm was staying and discover on security footage that Andrew was the last person to see Malcolm before he disappeared. Meanwhile, Juliet discovers that someone in her family played a part in the attack on Tessa and Siobhan admits to Henry the reason she faked her death.
After an attempt is made on Bridget's life, Agent Machado is determined to find who was responsible. Henry accuses Siobhan of putting a hit out on Bridget, while Bridget thinks Olivia was behind it. Meanwhile, Andrew admits to asking Malcolm to leave town and Juliet goes missing.