Cage plays a character called Charlie Kaufman, a fictionalised version of Kaufman himself. [Subsequent references will be to the character, not the real writer.] Cage also plays Charlie's brother, Donald, who is credited as co-writer of the film, though Donald Kaufman is a purely fictitious character. Charlie is hired to adapt a book, The Orchid Thief, into a screenplay; he hopes to produce a profound, true-to-life script, though he spends months on frustrated false starts. Donald, meanwhile, writes a formulaic thriller screenplay which is immediately optioned. Unable to create a compelling narrative from The Orchid Thief, Charlie decides to follow the book's author, Susan Orlean; surprisingly, her secret (and totally fictionalised) double-life is a far more fascinating screenplay subject, providing the character arcs and suspense that Charlie had dismissed as unrealistic.
Adaptation is incredibly self-referential, recalling films about the frustrations of filmmaking such as 8½ and Stardust Memories, and the novel Tristram Shandy (and thus the film A Cock & Bull Story). The film is not only about Charlie's Orchid Thief adaptation, it is his adaptation, as all of his ideas have been incorporated. His voice-over in which he runs through several potential film openings echoes Woody Allen's opening monologue in Manhattan.