From the track of poison, Conan discovers the trick of poisoning the professor to death. Conan solves the case and retrieves the secret that Akemi hid in the bathroom. It turned out to be a set of cassette tapes, recorded by Elena, Akemi and Ai's deceased mother, for Ai's birthday every year right up till the year she turns 20. The episode ended with Conan saying that Ai's mother was a true angel.