Another accident in Professor Bulfinch's laboratory, brought on by Danny, results in the creation of a transparent, resilient material. The material proves useful in creating a bathysphere, and Professor Bulfinch, along with his friend Dr. Grimes, Danny, Joe, and Irene, descends into the Pacific Ocean on an experimental voyage. Unfortunately, the bathysphere's pilot is rendered unconscious, and the bathysphere becomes trapped in a cave... Can Danny and his friends escape?

Danny Dunn on the Ocean Floor is the fifth novel in the Danny Dunn series of juvenile science fiction/adventure books written by Raymond Abrashkin and Jay Williams.