Episode 669: Treasure in the Tower of Darkness (Part 1)
Scenario: Ran's karate senpai, Kyodo Nanami, invites the Detective Boys for a treasure hunt at her home. Once there, they discover the fact that the treasure is very likely hidden in the Dark Tower. However, there aren't any entrances nor windows to enter the tower with. Around the estate, they also discover that this house has been equipped with various tricks and traps. Later, Nanami's mother, Kyodo Momoe, had been discovered dead, thought to have fallen from the tower. While investigating both cases, Haibara disappears, and the others also discover two secret entrances.
The Detective Boys meet Nanami Kyoudou, whose grandfather, Seitarou Kyoudou is the one who built "The Black Tower", rumored to have no entrance and treasure hidden within. Later, they visit her house, where Nanami Kyoudou's mother, Momoe Kyoudou is apparently pushed off of the Black Tower.
Momoe Kyoudou's body is found near the tower after her scream. Did she fall from the tower or did someone push her?
The Detective Boys, now even more determined to find an entrance, search the house, which is filled with different illusions. Then, Ayumi and Haibara needs to use the restroom. But after Haibara tells Ayumi to go ahead, she accidentally falls through a secret passageway hidden behind a mirror in the bathroom. Ayumi immediately alerts the boys about Haibara's disappearance, who begin investigating the restroom; consequently, Conan notices that there's wind coming from the mirror, but can't gain access into the passageway behind it. Mitsuhiko alerts Conan that there's a storeroom next door, so convinced that there's another entrance, the Detective Boys run next door to search the storeroom. There, they discover two mirrors: a big one connected to the wall (though appears to be leaning against it) and a smaller one sitting on a desk. While checking the smaller mirror, Ayumi notices that it is covered with the same heavy perfume Momoe Kyoudou was wearing, accidentally flips the mirror, and suddenly, the big mirror Conan was investigating slides down to reveal an entrance covered with masking tape. Through a small argument, Mitsuhiko and Genta accidentally fall through the passageway, leaving Conan and Ayumi alone. Conan asks Ayumi to stay, but she is determined to go with him to find Haibara, so holding hands, they go through the masking tape together.