The Stingray crew track the launch site of missiles fired on Marineville to a volcanic island. However, on investigating they become captured by the aliens responsible.

Troy locks horns with the boastful Naval Captain who arrives in Marineville to demonstrate a new missile. X20, however, loads the test missile with real explosives and it appears that the Naval Captain is actually out to kill Troy. Shore is ready to Court Martial the Captain until Troy proves the interference of Titan's subjects.

X20 has planted a bomb in the bass fiddle of a jazz group that will give a concert at the undersea city of Aphony, Marina's father. Troy uncovers the plot but is trapped in a burning shack. He escapes just in time and races to Pacifica in Stingray in an attempt to save the lives of his friends.

Investigating the disappearance of a robot probe, Stingray is drawn to the bottom of a volcano where two survivors of a destroyed city attempt to steal Stingray to escape the erupting volcano. When Marina locks the hatch they are forced to return for Troy and Phones who have been left to die. Since there are only two sets of breathing gear, Troy and Phones must rely on their WASP training to make the swim to Stingray.

After recovering a giant oyster, two explorers are captured by Troy in restricted waters. They persuade Commander Shore to let the Stingray crew help them collect it's pearl. However, the crew are unaware of their real intentions !!

Atlanta is taken captive by the crazed professor Cordo who rules a race of innocent underwater people. When Stingray arrives at his undersea farm he decoys Troy and Phones into a mock-up of Stingray while his subjects take command of the real craft and head for Marineville. Troy and Phones manage to overpower the professor in time to force him to recall Stingray before the creatures can launch their attack.

Atlanta is captured by an undersea race when Stingray investigates the collapse of an oil drilling rig. She discovers that the creatures only attacked the rig out of self-defence, believing that their home was under attack. Unfortunately, a bomb has been planted aboard Stingray that will explode when the ship dives. Atlanta makes a desperate effort to contact Stingray but, fortunately, Marina's pet seal, Oink, discovers the bomb and pushes it off in time

During a Terror Fish attack, Stingray is damaged. When Troy goes to make repairs, an Aquaphibian poisons him with some purple liquid. At Marineville, the doctors can't find a cure. Without treatment, troy will die within four hours. Titan has the antidote but will only send it exchange for Marina. Commander Shore refuses but Marina makes up her mind and returns to Titanica. Titan keeps his word and sends the antidote. Once recovered, Troy must come up with a plan to rescue Marina.

Professor Darren has developed a way to make gold from minerals on the sea bed. Agent X 2 Zero spies on the first test run & reports to Titan. Titan wants to destroy the Prof.'s Bathyscape & Stingray in one go when Stingray calls to collect the gold & deliver supplies to the Professor. Troy manages to save the mining operation & outsmart Titan once again.!

While waiting for Atlanta and Marina, Commander Sam Shore shows to Admiral Denver films showing the previous missions that Troy Tempest and Phones had with the submarine Stingray.