The story of Prot (Spacey), a mysterious patient at a mental hospital who claims to be from a distant planet called K-PAX. While his psychiatrist, Dr. Mark Fuller (Bridges), is baffled by this...

The story of Prot (Spacey), a mysterious patient at a mental hospital who claims to be from a distant planet called K-PAX. While his psychiatrist, Dr. Mark Fuller (Bridges), is baffled by this cheerfully confident man, Prot's descriptions of life on a planet 1000 light years away awaken a sense of possibility among the other patients. When Prot says he's going back before the summer ends, all the patients on the ward vie to go with him. As the days before Prot's announced departure from earth race by, Dr. Fuller struggles with questions of science versus faith and wonders about his own ability to distinguish reality from delusion.