Blood Work by Michael Connelly

The novel follows retired FBI agent Terry McCaleb, who is recovering from a heart transplant when he is approached by Graciela Rivers, the sister of the woman whose heart saved his life. Graciela believes her sister's death was not a random act of violence but a calculated murder. Driven by gratitude and a sense of obligation, McCaleb reluctantly agrees to investigate, uncovering a complex web of deception and danger. As he delves deeper, he discovers connections to a series of unsolved crimes, putting his own life at risk in a race against time to bring the killer to justice.