Gone, Baby, Gone by Dennis Lehane
It's hard to discuss too much of Lehane's novels without giving away several twists in the process. When Gone, Baby, Gone begins, Patrick and Angie have been having a prosperous year, sticking to lighter cases, avoiding the darkness that they witnessed and faced in Sacred and particularly Darkness, Take My Hand. After a four year old girl goes missing, her aunt decides to hire Patrick and Angie to help with the case. Despite hesitation and arguments against it (given the high profile case, the two investigators doubt they could add much to the case that the rest of the police force hasn't found), they eventually sign on due to the aunt's persistence.
Helene McCready, the missing girl's mother, is less than competent as a mother. Still, in the beginning, there are no suspects in the case, there are no known enemies. Angie and Patrick, however, quickly stumble upon a link between Helene and a drug dealer who was missing some money. Now that they have a motive, an exchange is scheduled which goes very wrong.
Angie continues to obsess over the case, and when another child goes missing a few months later, the media display takes up a lot of her attention. After everything they have been through in the past few novels, Amanda's disappearance as well as the other child's case still manage to have quite an effect on the pair.
One of the things that I like about Lehane's novels is that the heroes don't come away completely clean - they, too, have moral dilemmas and don't always make the right choices. Patrick continues to let himself be used to an extent as he occasionally takes a while to see the big picture and only sees what's immediately in front of him. He and Angie have both been hurt in the past few novels, and it has its effects - he has scars on his face, nerve damage in one hand, Angie still has scars from when she was shot etc. As much as Patrick likes his job, he also tires of it, and worries that it will consume him and what it means for his future. Given the topic of the novel, it is perhaps not surprising that Angie brings up children to Patrick which he is absolutely terrified of having in the world he's witnessed. While Lehane always answers the questions pertaining to the novel's specific mystery, he doesn't have happy endings. Depending on the novel, some are definitely more uplifting than others, such as Patrick, Angela and Bubba's knowledge that they always have each other to rely on, but even if the bad are occasionally punished, the good definitely don't live happily ever after.