A sudden car accident caused the dispatched staff member Hagio Harumi (Kitagawa Keiko) who went to Beijing alone to be hospitalized. During this period, she met the considerate and kind nurse Nishimura Reiko (Fukada Kyoko), who was considerate and diligently helped Harumi negotiate compensation with the driver Kudo Kensuke (Kora Kengo) and Kudo's friend Hasegawa Shinichi (Onoue Hiroyuki) in the insurance company. On the eve of discharge, Harumi invited Reiko, who was planning to resign, to share an apartment with her. The two girls were like-minded and very happy, and they also wrote a cohabitation diary together to communicate with each other. However, as they spent more time together, Harumi would occasionally find Reiko's occasional cold expression. Weird and terrible events happened alternately around them, and it seemed that Reiko also had a cold-blooded personality named Mary hidden in her body. She wanted to escape, but eventually found that everything was not as simple as she imagined... This film is adapted from the original work of the orthodox mystery writer Imaya Aya.