What is the ending of Keigo Higashino's "Masked Hotel"?

The ending of Keigo Higashino's "Masked Hotel" is that the wedding is held as scheduled, and the strange old lady who appeared once before appears again, and she still requires the services of a girl.

It turns out that she was the murderer in the fourth case. She deliberately planned to kill the heroine, the front desk girl, the old lady who pretended to be blind. She lost her heart because of the obstruction of the hotel service staff when she was young. The baby, therefore, takes revenge.

Extended information

Plot summary

Three murders occurred in Tokyo. From the unexplained sequence of numbers left at all crime scenes, the police deduced that this was a series of serial murders with warning information, and launched an investigation.

Kosuke Nitta (played by Takuya Kimura), an elite detective from the Metropolitan Police Department’s Investigation Section, deciphered that the number indicates the location of the next crime, and he speculates that the Cortesia Hotel in Tokyo will become the first one. 4 murder scenes.

However, there is no clue as to who the murderer is. The police therefore decided to sneak into Tokyo Cortesia to investigate, and Arata had to pretend to be a front desk staff to track down the murderer. The person assigned to guide him is Naomi Yamagishi (played by Masami Nagasawa), an excellent front desk employee at Tokyo Cortesia.

Faced with the continuous appearance of guests of unknown origin, Nitta, as a criminal police officer, "takes arresting criminals as his first priority" and tries to peel off the "mask" of the guests, while Shangmei, as a hotel staff, Starting from the principle of "ensuring the safety of guests as the first priority" and hoping to protect the "mask" of guests, the two are like fire and water.

Arata and Naomi clashed several times because of their differences in positions. However, as the latent investigation progressed, they gradually understood each other's values ??as professionals, and incredible trust began to develop between the two. relation. During this process, the case developed rapidly. Both the police and the hotel were cornered with no way out.