A prisoner is roused and escorted through Joliet Prison in Illinois. Is he on his way to the gallows? No, he's up for "standard parole". His personal items are returned to him, including a broken watch and prophylactics. The prisoner is released -- it is Jake (John Belushi). He meets his brother Elwood (Dan Akroyd). These are the Blues Brothers. Elwood has shown up in a used Plymouth police car after having traded in their old Cadillac for a microphone. Demonstrating the power of the car, with its cop tires, cop suspension, and 440 cubic-inch powerplant, Elwood convinces Jake that this is the new Bluesmobile.
They go see the Penguin, head nun at the Catholic orphanage they grew up in. She explains that they need $5,000 to pay taxes, or else the orphanage will be closed.
They meet up with their old friend and father figure Curtis (Cab Calloway) who advises them to "get yourself to church". They go to a Baptist church, where Reverend Cleophus James (James Brown) delivers an uplifting sermon. Jake "sees the light" realizing that he must put the Blues Brothers Band back together in order to raise the $5,000. Now they are on a mission from God.
The Bluesmobile gets pulled over. Through SCMODS (State County Municipal Offender Database System), the officers learn that Elwood has numerous outstanding traffic tickets and moving violations. The police intend to impound the car, but Elwood takes off, leading to a car chase. The Blues Brothers get away (destroying a shopping mall in the process), but now the Illinois authorities are searching for them.
A mystery woman (Carrie Fisher) blows up their apartment building, but they walk away from the rubble (as do the cops who were just about to apprehend them).
Trying to find their old band members, who have since taken other jobs, they visit a boarding house where one of the members had previously stayed. The lady doesn't remember where he went, but at the last minute she finds a business card with "Murph and the Magictones" on it. They find Murph and the Magictones playing at a Holiday Inn lounge. Murph and the others agree to rejoin the Blues Brothers Band.
Jake and Elwood visit the swanky Chez Paul restaurant, where another band member is maitre'd. The brothers behave offensively while eating a meal, tossing food and offering to buy women. Promising that they'll be back to eat breakfast, lunch, and dinner every day at this restaurant until he joins them, the maitre'd reluctantly agrees.
John Lee Hooker plays outside a soul food restaurant. Inside the restaurant, the brothers meet Matt 'Guitar' Murphy and 'Blue' Lou Marini. Matt's wife (Aretha Franklin) sings "Think", warning Matt to think about it before leaving the restaurant they own. Matt and Lou quit, and the band is complete. The band's first stop is Ray's Music Exchange. The proprietor Ray (Ray Charles) shows off the action in a keyboard, singing "Shake A Tail Feather". The band buys $1400 worth of instruments, on an I.O.U.
The Blues Brother's first gig is at Bob's Country Bunker, where the Good Old Boys are scheduled to play. Passing themselves off as the Good Old Boys, the Blues Brothers manage to play both types of music (Country and Western). They earn $200, but drink $300 worth of beer. They skip out, chased by the late-arriving Good Old Boys and Bob. They get away when the pursuing truck is t-boned by cops who have spotted the Bluesmobile. The cop deadpans, "boys, you are in big trouble".
The mystery woman fires a flamethrower at Jake and Elwood in a telephone booth, blowing up nearby propane tank. The brothers, still on their mission from God, emerge unscathed. In a sauna the next day, Jake and Elwood have a business meeting with promoter Maury Sline (Steve Lawrence) who agrees to book the Palace Hotel Ballroom for them tomorrow night.
Proclaiming "I hate Illinois Nazis", Elwood uses the Bluesmobile to force Nazis to jump off a bridge. Now they've gained another set of enemies, who vow to find them and kill them.
The word goes out on the streets -- Jake and Elwood swipe an enormous air-raid siren, strap it to the roof of the Bluesmobile, and use it as a loudspeaker to make announcements thoughout the city about the upcoming concert. They run out of gas. The local gas station is also out of gas. Elwood flirts with a chic lady (Twiggy) while waiting for the tanker truck to arrive.
The Blues Brothers Band play their concert at the Palace Hotel, beginnning with "Minnie The Moocher" as they wait for Jake and Elwood to arrive. Having heard about the concert, the authorities lead by Burton Mercer (John Candy) stake out the joint, planning to apprehend them after the show. Jake and Elwood sneak past the cops and join the band. The crowd is unmoved at first but are soon cheering. The band plays so well that a producer for a major record company offers them $10,000 cash as an advance on their first recording session. Jake and Elwood accept the offer and keep $5000, asking the producer to send $1400 to Ray's Music Exchange and to give the rest to the band. The brothers take off through a trap door in the stage while the band plays on.
The mystery woman confronts them in an underground tunnel, firing an automatic weapon at them. Pleading for his life, Jake removes his sunglasses for the first time in the film. She melts, smiles "oh, Jake", and kisses him. He pushes her to the ground, saying "let's go".
The police begin realizing the brothers are making their escape. Jake and Elwood are in the Bluesmobile with 106 miles to get to Chicago, a full tank of gas, a half pack of cigarettes, at night, and they're wearing sunglasses. An epic car chase begins as the Blues Brothers head towards Chicago to pay the taxes. Numerous police cars tumble off an embankment, and one ends up in a truck. As they approach the city, all authorities are alerted and "the use of excessive force is approved" in their apprehension. The chase continues in Chicago, reaching speeds of 110 mph on Lower Wacker Drive. Dozens of police cars continue to pile up. Hearing chatter on the police radios, the Nazis spot the Bluesmobile and give chase. The Bluesmobile stops at the edge of a highway overpass under construction, but the Nazis tumble over the edge. Jake and Elwood arrive at Daley Plaza just in time, as their car literally falls apart.
The police buildup continues absurdly, with National Guard units, helicopters, and SWAT teams getting involved. Jake and Elwood hastily make their way to the Cook County Assessor's Office, barring doors and sabotaging an elevator on the way. Hundreds of troops are in pursuit. They pay the taxes. The moment the tax receipt is handed to them they are handcuffed, surrounded by countless troops with pointed firearms.
The Blues Brothers Band play their next concert in prison, beginning with "Jailhouse Rock".