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 Captain Squid attacks Moby with his Shoctopus. Moby finds himself buried under a pile of rocks and the boys are locked within the pirate ship and unable to help their friend. Luckily for all, Scooby is still free and able to free Moby who in turn frees the boys. Meanwhile, Captain Squid is headed for Mystery Island to find the hidden treasure from the treasure map. Moby is able to pick up his trail and they boys are able to put the Electrifying Shoctopus out of commission with a giant magnet. Captain Squid is able to get away in his escape pod but the explosion of the rest of the ship destroys the treasure and the island. Moby and his pals have won again and are ready for their next adventure.