The setting is a zoo, or rather one of its parts is a terrarium. Even in such conditions, there will be circumstances for the creation of Sir Henry Merrivale's favorite mystery - the closed room. The deceased was found in a sealed (literally!) room, but many facts indicate that this was not a suicide. Despite the apparent impossibility of committing the murder and then sealing the room, everything was done quite simply... like a magic trick! However, like the secret of most tricks, the solution does not lie on the surface.