They are soon stranded on a small desert island and Duckula tries to think of some "ingenious" plan so they can attract someone's attention. After deliberating for a while, the entire desert island is enclosed by a glass dome and they are transported to the lost city of Atlantis. They are immediately arrested by some Mermen guards (who are actually fish). They say that Duckula is not permitted to return to the surface because the Atlanteans want the location of Atlantis to remain hidden from the outside world. One of the guards offers them a choice: Duckula, Nanny and Igor have to choose whether they prefer to live as slaves for the rest of their lives or face justice at the hands of the Atlanteans and their master, who, as it later turns out, is King Neptune himself.
Duckula decides he would rather have a fair hearing so they are escorted to King Neptune's courtroom. At first, Neptune comes to the conclusion that he wants to feed them all to the sharks as a punishment. However, when Duckula informs him that guard had offered them the option of enslavement before, Neptune has no choice but to honour the guard's offer. When the merman guard is about to chain them all together, Duckula decides to escape before he could do so. All three of them manage to escape by hanging on to Captain Nemo's ship, the Nautilus. Captain Nemo wants to throw them out because he says that he hates stowaways. But when the mermen pursue Nemo's ship the captain's thoughts are diverted. The mermen only stop pursuing them when Nemo's ship approaches the Kraken's lair. The Kraken grabs the ship with its tentacles and throws them back to the desert island. Duckula starts playing his harmonica, hoping too cheer everyone up, but ends up driving them crazy instead.
Igor, responding to Duckula's message in a bottle idea: "So all we need now, my lord, is a bottle, a piece of paper and something to write with."
Duckula (angry): "Do you know who I am?!?" The Merman guard responds "Why? Have you forgotten?"
Duckula: "Igor, do something." Igor responds "I am my lord, giving in to the inevitable."
Dmitri and Sviatislav: "Which fish made me an offer I couldn't refuse?... The Codfather!"
Captain Nemo: "It looks like a stowaway. And if there's one thing I hate more than Atlanteans, it's stowaways!"
- The Mermen are actually fish with a fishbowl as a helmet. Although they are fish, they require oxygen tanks in order to survive in Atlantis but Duckula, Nanny and Igor do not.
- Captain Nemo, also known as Prince Dakkar, is a fictional character created by the French science fiction author Jules Verne (1828–1905). Captain Nemo appears in Verne's novel, Twenty Thousand Leagues Under the Sea (1870), and his ship is called the "Nautilus".
- The hit 2018 animated film "Hotel Transylvania 3: A Monster Vacation" also features an entire segment with Count Dracula and his family in Atlantis.