The luscious hills of Koumi Island are one of many reasons tourists pay its shores a visit—a reason that comes second only to its scenic coral reefs and the legend of Anne Bonnie and Mary Read. The museum that houses the cutlass and pistol of the daring pirate duo does wonders for the small island's tourism.

On a trip to the island, the famous Kogorou Mouri is joined by his daughter Ran, her best friend Sonoko Suzuki, the Detective Boys, and Conan Edogawa. Following a mix up at the hotel regarding their rooms, the group encounters treasure hunters and becomes acquainted with the island's treasure fever. Sent on a hunt of their very own, the Detective Boys scour the isle; while in far harsher waters, Conan discovers a murder. The police, following a clue from a recent robbery, arrive soon after, and Koumi is plunged into chaos.

What follows is a mad dash by not only the treasure hunters but also the inhabitants of Koumi to secure Anne and Mary's long lost booty. All the while, however, Conan, Kogorou, and the police search for the one thing far greater than riches—justice.