James King, played by Will Ferrell, is a highly affluent hedge fund manager who is engaged to the stunning and ambitious Alissa, portrayed by Alison Brie. In a bid to improve their living situation, Darnell Lewis, played by Kevin Hart, and his wife, Rita, are striving to put their daughter Makayla into a better school, away from their crime-ridden neighborhood. Their lives intersect when Darnell unintentionally startles James in a parking lot, prompting James to deliver an inspirational speech about his rise to success. However, when he offers just a pair of singles as a "tip" from a hefty bundle of cash, the moment is both amusing and telling.
As Alissa throws an extravagant engagement party for herself and James, she presents him with an electric guitar and surprises guests by inviting John Mayer on stage. Their joyful moment quickly turns dire when the FBI barges in to apprehend James for fraud and embezzlement. Despite his lawyer Peter Penny’s advice for a guilty plea, James remains steadfast, believing in his impending exoneration. Unfortunately, he's sentenced to ten years in San Quentin and has just 30 days to put his affairs in order, during which his assets are seized, and he suffers the indignity of house arrest. In a desperate bid for freedom, he attempts to escape but finds himself abandoned by Alissa when she reveals she has moved on, prompting re-arrest by the police.
In a pivotal encounter, James once again meets Darnell, where he confesses his anxieties about prison life. In a stunningly misguided assumption, he asks Darnell, who he presumes has experience with incarceration due to his race, for guidance on how to survive behind bars. Darnell reluctantly agrees to train James in exchange for a staggering $30,000. However, Darnell's own knowledge of prison life is scant, leading to a series of comically ineffective training sessions that include pepper-spraying James and staging faux confrontations, to no avail.
As the days dwindle, Darnell determines that James must learn to defend himself in more intimate ways, leading them to a questionable rendezvous spot for James to encounter a man. However, James falters, proclaiming in front of captivated onlookers that he is willing to do "whatever it takes to get hard." The slapstick lessons continue, with James hitting the gym harder than ever and learning the art of smuggling contraband in the most peculiar places.
Time runs out for James as he prepares to join a gang for protection, leading him to an outrageous initiation that nearly costs him his life when his own identity as a wealthy businessman is threatened. Darnell, now convinced of James's innocence, decides they must uncover the real criminal—Martin, James's father-in-law and the true architect behind the embezzlement scheme. They embark on a high-octane mission to retrieve evidence from Martin’s yacht.
In a dramatic confrontation, James unleashes his newfound skills to take on goons while Darnell safeguards their only hope, the incriminating computer. The climax arrives as Martin confesses, with Alissa revealing her participation in the scheme. The duo attempts to escape on a life raft, only to be thwarted by Gayle, a hired gun, but not before the police arrive just in the nick of time.
Ultimately, justice is served as Martin, Gayle, Alissa, and Peter all face arrest, while James's own sentence is merely six months. When he’s released, he uses the experience to turn his life around, offering Darnell financial help to expand his car wash business for a brighter future. Together, they embark on a new journey, leaving the past behind.
