In order to solve the mystery of the second apostle, Shizuku must unravel the enigma surrounding the famous smile of the "Mona Lisa". During his investigation, he comes across an old acquaintance: the renowned novelist Maiko Natsuyagi! She asks for his help in decoding a strange poem signed by "Bacchus", as well as a mysterious black bottle with no label whatsoever. Could this bottle be connected to Leonardo da Vinci's painting? And what is Tominé looking for in the Taklamakan Desert?