Tom has Moby take him Tubb and Scooby to an old pirate ship that he had discovered on the ocean floor. The boys go inside the ship to explore and find a secret compartment in the Captain's quarters and discover a treasure map inside. They hear a noise and see the Electrifying Shoctopus, an octopus-shaped underwater craft piloted by Captain Squid. Captain Squid captures the boys and takes their newly found treasure map. Scooby escapes to find Moby, but will he be able to save the boys this time?