Arriving on the island, the five start searching the castle ruins to locate the old dungeons where the gold is hidden. Chasing a rabbit, Timmy falls down an old well, from where the children find the dungeon entrance. Exploring underground, they find the gold in a locked vault. Trouble soon arrives, as bad men come to the island hoping to steal the gold. They capture George and Julian, locking them in the dungeons and ask them to write a note to Anne and Dick who was up in the air to come back to the dungeons. George wrote the letter and Dick find something fishy about it as George signed her name as Georgina and decide not to go down. Unable to find Anne and Dick, they leave the island, taking the oars from the children's boat so they cannot escape. Anne and Dick use the good shaft to rescue Julian and George from the dungeon, and the children hatch a plan to trap the men when they come back to the island with a boat to steal the gold.