The Devotion of Suspect X

The Devotion of Suspect X (2005) by Japanese mystery author Keigo Higashino is the first novel in the bestselling Detective Galileo mystery series, which belongs to the honkaku genre (characterized by clever, logic-driven mysteries that give readers enough clues to solve the puzzle themselves). Higashino is one of the most popular writers in Asia and one of the most prolific mystery novelists in Japan. The series follows the genius physicist Dr. Manabu Yukawa, who consults with the police to help solve particularly difficult cases. Subverting the usual order of a mystery novel, The Devotion of Suspect X reveals the perpetrators of the crime in the first chapter, in which divorced mother Yasuko kills her abusive ex-husband. Ishigami, Yasuko’s neighbor and unrequited admirer, covers up the crime. What follows is an intricate cat-and-mouse game as Yukawa attempts to uncover the truth while Ishigami, a high school mathematics teacher, uses his similar genius to stay one step ahead of him. The novel explores The Morality of Love and Self-Sacrifice, the difficulties of Navigating Imperfect Justice and Moral Ambiguity, and the Inherent Worth of Individuals.

This guide is based on the 2011 paperback edition published by Minotaur Books and translated by Alexander O. Smith.

Content Warning: The source text and this guide contain depictions of domestic abuse, gender discrimination and sexual harassment, suicidal ideation and self-harm, attempted death by suicide, graphic violence, and death.

Plot Summary

As high school math teacher Tetsuya Ishigami follows his daily routine, he walks along the Sumida River and passes a tent city of unhoused people on his way to Benten-Tei, a lunchbox shop where his neighbor, Yasuko Hanaoka, works. Yasuko is a divorced single mother with a daughter named Misato. Ishigami is infatuated with Yasuko but rarely speaks to her.

Later, Yasuko’s abusive ex-husband, Shinji Togashi, appears at Benten-Tei while she is alone and attempts to extort money from her. She refuses. That night, he follows Yasuko home and threatens both her and her daughter, Misato. Misato lashes out and hits him with a vase. Togashi becomes violent, and Yasuko and Misato kill him together. In the aftermath, they argue about whether to turn themselves in. Ishigami hears the commotion next door and offers to help. He takes care of all the details, disposing of the body and instructing Yasuko and Misato how to create an alibi and how to behave when the police inevitably arrive.

When a body is discovered on the banks of the Old Edogawa River, Detective Shunpei Kusanagi is brought in. The body has been stripped, its face disfigured, and its fingerprints burned off to hinder identification. However, a bicycle is found nearby. From clues left on the bicycle, Kusanagi and his team identify the body as Shinji Togashi, who died on the night of March 10. Kusanagi believes that Yasuko is the most likely suspect. However, when he cannot disprove her alibi, he turns to his friend, Dr. Manabu Yukawa, for advice. Yukawa is a physics professor at the local university who has consulted on several cases for the police at Kusanagi’s request.

Yukawa makes no promises to help Kusanagi. However, Ishigami was also a college friend of his, and he respected the man, believing Ishigami to be even more intelligent than himself. Now, when he visits Ishigami to reminisce about their college days, he soon grows to suspect that Ishigami is involved in the murder, though he will not tell Kusanagi why he believes this to be true.

The police continue their investigation, constantly questioning Yasuko and Misato, investigating their lives, and following their movements. Each night, Ishigami calls Yasuko’s cell phone from a payphone to check in. He has accurately predicted each action that the police take, and he has planned accordingly. Yasuko is impressed by how well he is handling the situation, but she pretends not to understand that he is doing all of this because he has romantic feelings for her.

An old friend of Yasuko’s, Mr. Kudo, hears about the murder and visits to offer his support. The two begin dating. Ishigami watches silently and writes anonymous threatening letters to both Kudo and Yasuko. Kusanagi notices that Yukawa is investigating Ishigami on his own and demands to know why, as Kusanagi still believes Yasuko to be the real suspect. Yukawa does not want to believe that his friend Ishigami could kill anyone, so he resists giving Kusanagi any answers until he is certain. Meanwhile, Ishigami also notices Yukawa’s suspicion and becomes afraid; he was not worried about the police, but he now fears that Yukawa will uncover the truth.

In a sudden twist, Ishigami turns himself in to the police and confesses to Togashi’s murder. He concocts a story about being Yasuko’s bodyguard, with the intent of appearing to be a delusional stalker. The anonymous letters that he previously sent to Yasuko and Kudo support this theory. However, neither Kusanagi nor Yukawa are convinced that this is the truth, so they continue investigating.

Finally, Yukawa puts the clues together and confronts Yasuko. He realizes that even she does not know the truth, and he asks her if she ever thought it strange that the police kept asking for her alibi on the night of March 10 when she killed her ex-husband on the night of March 9. He explains that to ensure that Yasuko would not be caught, Ishigami did not merely cover up Togashi’s death but murdered a second man: one of the unhoused men whom he walks by every day. Ishigami then disguised the dead man as Togashi in order to confuse the time of the death and Yasuko’s whereabouts. In short, Ishigami made himself a genuine murderer just to protect Yasuko.

In a flashback, Ishigami remembers the day that Yasuko first moved into his apartment complex. At the time, he was depressed and was preparing to die by suicide, and he had the rope in his hand when Yasuko and Misato knocked on his door to introduce themselves as his new neighbors. He took this occurrence as a sign to keep living. From that moment, he fell in love with Yasuko and swore to protect her and repay her for saving his life.

Horrified by the sacrifice that Ishigami has made on her behalf, Yasuko arrives at the police station to turn herself in. Ishigami sees her arrive and realizes that everything he has done was for nothing. He screams as Yukawa stands by his side.