A Manhattan psychiatrist thinks he's seen it all until he's assigned to analyze Prot, a psychiatric patient who claims to be from a distant planet called K-PAX. He is convinced that Prot is "a convincing delusional," but his cynicism turns to open-minded fascination as Prot's case reveals a combination of otherworldly insight and all-too-human trauma, prompting an earthbound explanation for Prot's allegedly alien origins.