In the thirteenth episode of Magic Island, titled 'Joan Stays on the Yacht', the expedition aboard the Gregory yacht has taken a dark turn. After successfully locating a lost girl on the mysterious island of Euclidia, the crew now finds themselves trapped, unable to sail home. The mad scientist G-47 has thwarted their plans, leaving them feeling more like prisoners than adventurers. As they gather in Mrs. Gregory's cabin, the atmosphere is thick with tension and uncertainty. The crew realizes that their attempts to communicate with the outside world have been compromised, and the threat of G-47's powerful weapons looms over them.