Kaito's the thief and the cop's daughter is hunting him, except she has no idea she's traveling with her target. Conan knows exactly who Kaito is and shows up anyway. The entire OVA is three people on the same train playing a game where only one of them knows all the rules, and that person keeps switching depending on which door you're looking at.

A train running from Tokyo to Osaka becomes the stage for a heist when Inspector Ginzou Nakamori and his daughter Aoko ride along to help stop Kaitou KID from stealing the Crystal Mother. The prize is Europe's largest topaz, owned by Queen Selizabeth of the Principality of Ingram, who is aboard. What neither Aoko nor her father realizes is that their companion Kaito is KID himself, and he will do whatever it takes to get the jewel. His task is harder than usual, because the Queen has already hidden the gem somewhere on the train. Conan Edogawa is also among the passengers, along with a little boy named Philip, and both are set on stopping the phantom thief. Suspecting a strike is coming, Conan starts investigating on his own.