This episode begins with Jake once again flying in bad weather. This time his passenger is an American scientist, Johnny Kimble, who Sarah believes is defecting to the Nazis. En route to Boragora they spot an outrigger full of dead or dying natives. They stop to help, and Jake swims through shark-infested water to save the lone survivor who is clutching a metal canister (containing glowing radioactive S-90). The native later dies (of radiation burns) and Kimble steals the canister from Corky. Sarah is determined to stop Kimble from meeting the Germans, so she gets him drunk and lures him to her room. There she slips him a mickey and takes the canister. Jake come to the door, inadvertently allowing Reverend Willie to steal the canister. Sarah later finds out the Kimble is an American agent, not a defecting scientist. However, he's still out cold. Jake offers to pose as Kimble for the meeting with the Germans. He accompanies them back to the island where they are conducting secret experiments to make an atomic bomb, the "Black Pearl." Willie sees Jake go with them and regretfully informs the Nazis that he's an impostor. It's time to detonate the bomb, so they leave Jake on the island. Corky and Sarah show up in the nick of time and they tow the bomb to the lagoon which just happens to be the deepest part of the Pacific. The bomb safely detonates, and they return to Boragora to fill-in the now-conscious Kimble on the bomb.
The plot of this episode is a lot more sophisticated than many other episodes, and the writing and acting are steadily improving. Also, this episode once again presented an opportunity for Jake to disrobe, this time as he changes into Kimble's clothes. Sarah looks demurely away, but the rest of us can pause the DVD for as long as we like.
Science fact: The S-90 of the episode is really Strontium-90 (Sr-90). S-90 would be Sulfur-90, which doesn't exist. However, there are radioactive isotopes of Sulfur such as S-35 which I've used many times in DNA sequencing. It doesn't glow blue.