John Burns (Dan Aykroyd) is a patient at a mental institution who gets an unexpected shot at freedom when circumstances find him mistaken for a colleague of Dr. George Maitlin (Charles Grodin). Sneaking out of the facility, Burns poses as his psychiatrist on a radio show in Los Angeles, which leads to great ratings for the program. Burns also finds a new friend in homeless eccentric Donald Becker (Walter Matthau), but his good times are threatened when Maitlin discovers the ruse.