Ironside's friend Carl Anderson, a psychologist, has collected examples of art from five San Francisco artists. Following a chess match, he offers Ironside a different challenge: one of the artists is in a dangerous state of mind, where just a slight shift could lead to murder. Forty-eight hours later, Ironside returns to his friend's house. Anderson has been knifed to death, taking to his grave the answer to his tantalizing question. Ironside is more determined than ever to puzzle his way through the artists' minds to the truth.