Helen Cadmus was dead - but how had it happened?
Suicide, most people said. She jumped off that millionaire's yacht in a fit of despair, her body was never found, and the case was closed. The story was too neat to suit Perry Mason. It didn't add up. Somebody was concealing the truth about Helen's death, and how was going to uncover it even if it killed him.
That's how Mason fell into a trap set by three killers - two humans and one grinning gorilla!