In 1959, the shocking discovery of the four lifeless bodies of the Clutter family on their Kansas farm sends ripples through the nation. As he reads about this tragic event in The New York Times, Truman Capote, played by Philip Seymour Hoffman, becomes deeply fascinated and immediately contacts the editor of The New Yorker, William Shawn (portrayed by Bob Balaban), revealing his intention to document this harrowing story.
Capote makes his way to Kansas and invites his childhood friend, Nelle Harper Lee, to accompany him. His goal is to gather insights from individuals associated with the Clutter family, with Lee acting as his intermediary. Although Alvin Dewey (played by Chris Cooper), the lead detective from the Kansas Bureau of Investigation, initially dismisses Capote's requests, his wife, Marie (Amy Ryan), who admires Capote's literary work, convinces her husband to invite the pair over for dinner.
During their dinner gathering in January 1960, as Capote shares captivating stories about glamorous movie sets and Hollywood icons, he gradually wins over Dewey. This leads to a unique opportunity where Capote gets to lay eyes on photographs of the deceased victims. The mood shifts abruptly when murder suspects Perry Smith (Clifton Collins Jr.) and Richard "Dick" Hickock (Mark Pellegrino) are apprehended. Through a combination of charm, persuasion, and a keen understanding of human emotions, Capote successfully secures visits to the prison where the suspects are held.
While uncovering the details surrounding the case, Capote discovers that both Smith and Hickock had waived their rights to a preliminary hearing, believing it might "curry favor with the judge." As he interacts more with Smith, he begins to forge an unexpected emotional bond with him. Capote shares his ambition to transform the articles into a full-length book with Shawn, despite the ambiguous legal proceedings taking place.
As the trial concludes and both suspects receive death sentences, Capote's access to them continues, buoyed by his dubious generosity inviting Warden Marshall Krutch (Marshall Bell) to benefit from more privileged visits. Particularly attentive to Smith, who has fallen into a state of despair, Capote takes it upon himself to bring comfort, including feeding him baby food to restore his health.
Over subsequent visits, amidst his literary endeavors which include a year away in Morocco and Spain with his partner Jack Dunphy (Bruce Greenwood), Capote delves deeply into Smith's turbulent past, reflecting on the conflicting emotions stirred by the gruesome circumstances. Flawed as it may be, Capote's pursuit to grant Smith and Hickock better legal representation results in protracted appeals, ultimately frustrating him as he finds it increasingly challenging to obtain the definitive account of the night of the murders from Smith.
Tensions escalate as Dewey expresses his anger and threatens repercussions, but the real strain manifests when Smith questions Capote, who evades the inquiry about revealing his book to him. Feeling increasingly ensnared by a narrative without closure, Capote realizes he cannot complete his book until the legal proceedings are resolved. After much deliberation, Smith finally recounts the horrifying events leading to the deaths of the Clutter family, yet in this moment of clarity, Capote grapples with his moral dilemma, withdrawing legal support and leaving the men to face the court alone.
With his narrative now within grasp, Capote remains ensnared, tied to an unresolved legal battle, preventing him from publishing his much-anticipated account. Meanwhile, Lee's acclaimed novel, To Kill a Mockingbird, garners massive success as it leaps to the silver screen, a triumph that brings Capote no joy as he spirals into his personal demons fueled by alcohol.
As their final appeal is struck down, Smith fervently implores Capote for a last visit prior to his scheduled execution on April 14th, 1965. Overcome with guilt, Capote hesitates but is ultimately compelled by a moving telegram from Smith directed to Lee, leading him back to Kansas, where he becomes an unwilling participant as Smith and Hickock face their grim fate.
Upon returning, Capote confides in Lee about the harrowing ordeal and expresses profound regret over his inability to intervene. She notably responds, "Maybe not. The fact is you didn't want to." In the concluding scenes, Capote reflects over photographs and remnants of the case, laying bare the complexity of his journey. The epilogue reveals that while In Cold Blood catapulted Capote to unprecedented fame as America's preeminent writer, he subsequently struggled to replicate his earlier success, eventually succumbing to alcoholism in 1984.
