Koumi Island is known for its stunning coral reefs and Anne Bonnie and Mary Read's legendary tale, but the lush hills draw in just as many tourists. The small museum that displays the pirate duo's cutlass and pistol is a hit with visitors seeking adventure. Famed detective Kogorou Mouri, his daughter Ran, her best friend Sonoko Suzuki, and the Detective Boys get caught in trouble during their island getaway when their hotel rooms are switched. They face treasure hunters and the island's craze for riches, but Conan Edogawa becomes embroiled in a murder in rough waters. As Koumi's police investigate a recent robbery, chaos ensues, and everyone scrambles to find the treasure. The treasure hunters and locals clash in their pursuit of Anne and Mary's lost riches, but Conan, Kogorou, and the police seek justice, not wealth. With madness overtaking Koumi, the race to uncover the truth begins.