Dr. Malcom Sayer (Robin Williams) is a new neurologist in charge of a ward of catatonic patients who have been nearly comatose for thirty years after an encephalitis epidemic. He gets permission to try a new drug, L-dopa, which initially has remarkable results. The first patient he tries the new treatment on, Leonard Lowe (Robert De Niro), suddenly becomes alert and aware. Leonard must now come to terms not only with what has happened to him, but to life in the new world in which he has awakened. Buoyed by his initial success, Dr. Sayer starts treating the other patients who also emerge from their catatonic states. Dr. Sayer then notices new symptoms in Leonard, and fears that the L-dopa effects will not last.