Ran and Sonoko brought Conan to an indoor tennis court. While Ran and Sonoko are playing tennis, Conan goes to the bathroom. As he is leaving, he hears a slap from the next room. He peeks into the room and see's a man named Takao Goto and a woman named Yuka Tsuchida arguing. Apparently Yuka is angry that Goto invited Sonoko as she thinks he wants to ditch her for Sonoko. As he apparently fixes everything up with her he leaves. She starts kicking the lockers saying, "Don't you dare leave me!" Meanwhile, Ran is looking for Conan where she meets one of the spectators named Azuma Fumihiro, who tells her he went to the restroom. Later, Takao is dead. Who is the murderer?

Two people have been murdered in sealed rooms. While investigating, police discover others have been receiving threatening messages and believe the sender is likely the murderer as well.