Tom, Tubb and Scooby are water skiing behind their friend Moby when they notice what looks like a space capsule about to splash down in the ocean. Manta Menace is waiting for the capsule and it's contents, the secret maps of the Mars diamond mines. The boys see the capsule sink and have Moby take them in so they can investigate. Manta Menace spots them and begins firing torpedoes. Who will win this underwater battle?