The Devotion of Suspect X (容疑者Xの献身, Yōgisha Ekkusu no Kenshin) is a 2005 novel by Keigo Higashino, the first in his Detective Galileo series and is his most acclaimed work thus far.

The situation quickly escalates into domestic violence, prompting Yasuko and Misato to kill Togashi in self-defense.

Overhearing the commotion, Ishigami, who is secretly enamoured of Yasuko but has never told her so, offers his help, disposing of the body and plotting the cover-up of the murder step-by-step.

When the body is discovered and identified, Detective Kusanagi, who was initially investigating the disappearance of Togashi, is assigned the case and Yasuko comes under suspicion.

The book ends with her meeting Ishigami in jail, revealing that she and Misato have confessed to killing Togashi and are determined to serve their sentence together with him, leaving him in tears.