Troy and the Stingray crew are assigned to retrieve a large pearl from an over-sized oyster, but Marina seems uneasy about the whole ordeal.
Two divers, Mike Bromley and Chick Kingsland, are exploring an underground cavern. As they swim, unstable rocks nearby create a rockslide, which Bromley nervously hopes won't block their path. They eventually come out in a large open cavern with a large oyster in the middle surrounded by man small ones. There is a legend that there is a very large and valuable pearl in the center, which is what they are after. Due to the oyster's size, which makes it impossible to open, and outdated equipment which gives the two a very limited supply of air, they are unable to wait for it to open and are forced to return to the surface.
Right as they surface, Stingray approaches their boat and Captain Tempest hails them. Bromley and Kingsland are diving in an area protected by the WASPs for oyster farming, and Tempest escorts them and their boat out of the area, before bringing them to Commander Shore at Marineville. Commander Shore dismisses their explanation of the supposed pearl as nonsense, but Troy and Atlanta manage to convince him otherwise, for as Atlanta says, WASP uses crushed pearls to insulate their radioactive isotopes.
The crew of Stingray and the pair of treasure hunters set out aboard the sub to recover the pearl. Marina doesn't want to go on the mission-she indicates that the pearl is a "bad omen" to her people. Troy dismisses her concerns, but she is unconvinced.
After Stingray lands on the bottom, Troy and Bromley exit and go to recover the pearl. A rockslide blocks their path, but Troy convinces Bromley to clear the rocks, even though it uses up an hour of their air supply. On the way back, both run out of air, but Phones manages to get a spare air supply to both before they drown. Back on Stingray, Bromley and Kingsland immediately threaten the crew at gunpoint and force them to leave the sub. Troy reluctantly agrees to protect his crew. Meanwhile, a large number of the smaller oysters in the cavern have left the bottom and appear to be moving towards Stingray.
With a limited supply of air in their diving gear, Troy and Phones make for the surface as the hapless Kingsland and Bromley try to figure out the controls with oysters closing in. They settle in Stingray's turbine, jamming it, and then begin to settle on the rest of the sub. Marina, after making sure that both men made it to the surface safely, returns to Stingray to witness all of the oysters settling all over the sub. Bromley and Kingsland realize how much danger they are in when the engines won't respond and the hatches are all sealed shut by the attacking oysters. They desperately radio Troy for help, who has returned with his crew at the insistence of Marina, only to find his ship covered in oysters.
Troy realizes that the pearl is attracting the oysters, and tells the terrified men on board to shoot both the pearl and their guns out of the missile ejection tube. After the pearl is shot out of the tube, the oysters immediately follow it and settle around it on the seabed. Troy and Phones board Stingray and retake their ship. An angry Troy holds both men at gunpoint and tells them they will be spending time in the Marineville jail, and asks Marina to tie them up. However, Marina is nowhere to be found-she has taken the pearl back to its rightful place, the giant oyster.
Regular Voice Cast
- Captain Troy Tempest - Don Mason
- Lieutenant Phones Sheridan - Robert Easton
- Lieutenant Atlanta Shore - Lois Maxwell
- Commander Sam Shore - Ray Barrett