A fog-draped morning, Tsuna is called out to Nami Junior High (?) by a mysterious phone call. On the way there, he runs into Yamamoto, Ryohei, and Gokudera. It turns out that Gokudera had come looking for Tsuna, but Yamamoto and Ryohei had been called out by the same kind of mysterious phone call. Is this one of the Arcobaleno’s tests…? They await suspiciously, and before them, Mammon—or Viper—of the Arcobaleno appears. Mammon says he has taken Kyoko hostage. Regardless of Tsuna and the others’ distraught faces, Mammom coldly kicks off a new mystery-solving game.