The Bears are back in Rocky Bay for another holiday. This time, they run into their old friend, Captain Binnacle, who invites Rupert to join him for a ride in the bay in his new boat.
The first thing the sailors find on their voyage is an island where there’s never been an island before. Second, they meet a merboy, Finian, who followed them to get back a shell he lost on the beach that Rupert collected. Third, all the sea creatures nearby start fleeing for their lives from something attacking their home. Fourth, they discover the island is actually a disguised ship… oops, motorboat (sorry, Captain), equipped with a ray gun and giant vacuum its driver is using to search for sunken treasure. Finally, the person running the ship is none other than Rupert’s old enemy from Egypt, Sir Humphrey Pumphrey! Once again, it's up to Rupert and his friends to stop him from stealing treasure, this time from Rupert's old friend King Neptune himself!
Marks the first of only three times in the series when a villain makes a second appearance.
This episode provides examples of:
- Arbitrary Skepticism: Sir Humphrey has a talking eel henchman and captures a merboy, yet he finds the existence of the legendary Neptune hard to believe?
- Bad Boss: Sir Humphrey is no nicer to Snipe than he was to his last henchman.
- Cassandra Truth: Neptune's chamberlain initially refuses to believe Rupert's and Finian's claim that a Topworlder could actually pose a threat to Neptune's palace.
- Chase Scene: Ensues after Rupert and Finian get off the motorboat with the pearl.
- Chekhov's Gun: The pink shell Rupert picks up and finds particularly beautiful turns out to belong to Finian and is the reason why the merboy follows them and ends up meeting Rupert.
- Continuity Nod: Rupert and Humphrey both refer to their previous meeting in "Rupert and the Nile."
- Demoted to Extra: Captain Binnacle and the Merboy are both frequently recurring characters in the comic strip, but both make their only appearance in the show in this episode.
- Distressed Dude: Finian gets captured and tied in a net by Sir Humphrey.
- Green Aesop: Before resorting to attempted murder and theft, Sir Humphrey’s treasure hunt would have been crime-free, if he used a more efficient method than blasting pieces of rock and reef to smithereens and vacuuming up the sea floor.
- Hold Your Hippogriffs: Finian uses the phrase "scaredy catfish."
- I Am Not Weasel: Small variation — Finian fruitlessly reminds Sir Humphrey multiple times that he's not a "mermaid."
- Insistent Terminology: Captain Binnacle won't stand for anyone calling Sir Humphrey's "motorboat" a ship!
- Intergenerational Friendship: Rupert and Captain Binnacle
- Island of Mystery: The mystery is its sudden appearance out of nowhere.
- Mineral Macguffin: A giant pearl lights the palace, allowing merpeople and sea creatures to live so deep in hiding from the surface. As the most eye-catching treasure, it's what Sir Humphrey wants the most.
- Never My Fault: Sir Humphrey blames Snipe for everything that happens that he doesn't like, even stuff he had nothing to do with like Finian escaping with Rupert.
- Nice Job Breaking It, Hero: Granted, it's understandable that Rupert and Finian go to warn King Neptune, but before he spotted them, Sir Humphrey wasn't able to find the palace. The boys led him right to it!
- Saying Too Much: Finian tries to scare Sir Humphrey by telling him he's been destroying the sea right near King Neptune’s palace. This news immediately motivates Humphrey to go looking for the palace so he can steal the king's treasure.
- Seen It All: Rupert's met merpeople before, so he's not nearly as surprised at the sight of Finian as Captain Binnacle is.
- The Little Shop That Wasn't There Yesterday: The little island definitely wasn't there yesterday.
- Named by the Adaptation: The Merboy.
- Traveling Landmass: Said mystery isle is actually just a ship… er, motorboat in disguise, so, naturally, it's always moving.
- Would Hurt a Child: Sir Humphrey's first move when Finian tries to stop his vacuum is to turn his ray gun on him. He's also clearly trying to kill both boys when shooting at them during the climax.
- You Meddling Kids:Sir Humphrey: Time to take care of that meddling bear once and for all!
