Elmer and his friends, Karen and Oscar, are eager for school to end and summer vacation to begin. Their teacher, Mr. Bigelow, warns the class to beware of their enemies, the shark and the moray eel. He also informs them not to go into the Forbidden Territory where there are traps and nets.
As soon as school is out Elmer and his friends ignore the teacher's warnings and go directly into the Forbidden Territory to explore the traps. When Elmer gets caught in a trap, Karen and Oscar don't expect it to move swiftly away from them. They hurry home to get help by telling Elmer's parents about the frightening incident.
Find out what happens to Elmer as the trap moves swiftly along the bottom of the ocean, stopping frequently to catch octopuses, who have carelessly entered the Forbidden Territory.
