Five boys – Donald "Duck" Matthews [Robert Townsend], Anthony "Choirboy" Stone [Tico Wells], J.T. Matthews [Leon], Terrence "Dresser" Williams [Harry Lennix], and Eddie King, Jr. [Michael Wright] – perform at a Battle of the Bands contest as The Heartbeats. They don’t win, losing to Flash and the Ebony Sparks, but their energetic set wins over the crowd and grabs the attention of Jimmy Potter [Chuck Patterson], a savvy manager who offers to steer them. He promises them $100 if they don’t win the next month’s battle; when the Heartbeats still lose, Jimmy makes good on his word. The owner of a local club then asks to hire them, and the Heartbeats decide to let Jimmy handle their future.
Bird [Roy Fegan] and The Midnight Falcons watch the Heartbeats rehearse and fear being upstaged; Bird enlists his girlfriend to rally friends for a boisterous welcome that teases and taunts the Heartbeats while cheering the Falcons. The announcer—cousin to one of the Falcons—forces the Heartbeats to rely on a house piano player. Duck grows frustrated with the pianist’s routine and takes the stool for himself. Eddie leads a performance that brings Bird’s girlfriend to tears in his arms. The Heartbeats win the contest and catch the eye of Big Red Davis [Hawthorne James], the powerful owner of Big Red Records. Big Red extends a deal, but Jimmy Potter and Eleanor Potter [Diahann Carroll], wary of corruption in the label, decline. The Heartbeats instead issue their first single on Jimmy’s independent label and search for a trustworthy partner, only to find that most labels aren’t interested—except a company that wants to buy Duck’s songs for a group they’ve already signed, The Five Horsemen [Roger Rose]. Faced with limited options, the Heartbeats sign with Big Red.
Their road tour is marred by racism and tough living conditions, yet they press on. Dresser's girlfriend visits and reveals she is pregnant, adding emotional weight to their climb. The album cover photos become a flashpoint: the initial approval shows the Heartbeats as a black group, but the released cover features white faces, highlighting the persistent racial tensions shaping their career.
Across the mid-to-late 1960s, The Heartbeats rise with awards, chart hits, and magazine covers. Eddie fights demons of alcohol and cocaine, and his struggles affect performances and strain his relationship with his partner Baby Doll [Troy Byer], who ultimately leaves him. Convinced Jimmy intends to eject him from the group as Eddie’s condition declines, he makes a deal with Big Red to sever Jimmy from the contract. Jimmy threatens to expose payola, bootleg deals, and other shady practices, spurring Big Red to have him killed. After Jimmy’s funeral, the Heartbeats learn that Eddie’s deceit precipitated the fraying alliance between Jimmy and Big Red. Big Red is convicted of Jimmy’s murder, forcing the Heartbeats to sign with a new label. Grappling with guilt, Eddie leaves the Heartbeats and sinks deeper into poverty and substance abuse.
The Heartbeats recruit Flash [John Canada Terrell] as their new lead singer. Duck suspects his fiancée, Tanya Sawyer [Carla Brothers], of infidelity and tails her to a hotel, only to discover she’s meeting with J.T. rather than Choirboy. Tanya’s past relationship with J.T. predates her romance with Duck, but she now insists she’s in love with him. J.T. urges her to be honest, but she refuses. At a major awards ceremony celebrating their success, Flash announces a solo move, and Duck reveals he knows about the affair between Tanya and J.T., prompting his departure and the eventual disbanding of the Heartbeats.
In the early 1990s, Choirboy returns to singing in his father’s church. Eddie becomes sober after embracing Christianity, marries Baby Doll, and finds a role guiding his own group while still contributing songs through Duck’s writing. J.T. is now married with a wife and two children, including a son named "Duck," and the brothers begin to reconcile. Flash remains the lone Heartbeat who has sustained a sustained career, shifting from doo-wop to pop with Flash and The Five Horsemen.
At a family gathering, the former Heartbeats reunite with their loved ones to reminisce and perform old moves. Eddie, initially hesitant, is forgiven by Eleanor as she comes to terms with the losses and deaths that shaped their journey, closing a chapter on the past while leaving room for forgiveness and memory.
