Conan and the Detective Boys run into a man who had a knife in his hand and was being chased by a police officer. The man grabs Ayumi and faints while whispering something into her ear. Conan and the Detective Boys accompany the man and the police to the hospital and learn that he had some contusion on his head and the police officer was chasing him because he seemed suspicious.

Bourbon and Conan help with the investigation and arrive to the conclusion that the culprit must have switched her cup with the victim in order to poison her. There is one problem though: each one of them is drinking a tea of a different color.