Reading of the brutal murder of an entire family on a farm in Holcomb, Kansas, startles Truman Capote, a reporter for The New Yorker magazine, and he goes there to cover the story. What he finds is a murder without an identifiable motive, and, shortly thereafter, two men on death row for the murders who couldn't be more different. He befriends Perry, one of the two, and is befuddled to find an erudite, sensitive man, and Capote struggles to understand how such a man could be guilty of such crimes. Still, there is little doubt of Perry's guilt, for Dick, Perry's far less cultivated accomplice,has spoken of the murders in Capote's presence, though not admitting the murders were premeditated, and Perry makes no attempt to deny his participation.
Capote is so troubled and fascinated by the murders that he resolves to write a book about the incident. The problem is that the quality of his book will suffer unless he can learn what really happened on the night the crimes took place, as he would be unable to answer the very question that compelled him to devote so much time and effort to studying the murders.
Capote grows closer and closer to Perry, and their growing relationship and Capote's obsession with the successful completion of his project appear to motivate his attempt to intervene in the case and delay Perry's execution. In his prison visits to see Perry, he must delude him into believing that he is trying to get him a new trial and a fresh chance at acquittal. In truth, Capote's actions are self-serving, but the result is that he and Perry grow closer, and, eventually, Perry relates what really happened the night of the murders. An armed robbery went wrong, and the murders had been committed in the rage of the moment by Perry, who had been goaded by his accomplice, Dick, to kill all possible witnesses to their crime. Now in possession of the truth, Capote withdraws from the scene, perhaps understanding that the executions will now provide the final chapter of his book.
Not long after, Perry and Dick are executed, but Capote has already succeeded in understanding the Holcomb murders, and is ready to write a novel that will be celebrated as a masterpiece.