The Detective Boys participate in a kite competition, hoping to advertise their business. Ai hums a tune that gets the others curious as to what she is listening to, but she says that's a secret, challenging Conan to try to figure it out. Conan plans to have Ayumi try to record it, but she accidentally reveals to Ai the trick but then realizes she had lost her phone. During the competition, one of the guys who had attracted trouble with some of his associates as well as his wife is backing up while holding a kite, but falls over a high ledge into a river where he nearly drowns. Conan and the kids suspect foul play, especially when they discover the lengths of the rope barrier do not match.