Devil and the Deep Blue Fish by Amy Lane

PI Jackson Rivers and Henry Worrall have gotten used to throwing themselves into danger as a team, so when Henry is hurt badly one night defending a friend and her teenage ward, it’s all hands on deck for Jackson, his fiancé Ellery Cramer, their firm, and their friends. Henry is battling for his life. The least they can do is hunt down Henry’s shooter and keep the intended victims safe.

Knowing Jackson will dedicate himself to tracking down a very dangerous assailant with no regard to his own safety, Ellery makes one stipulation: Jackson needs a temporary partner. Jackson finds a good one in someone from the firm’s past, but while Jackson’s figuring out a new rhythm on zero sleep and a lot of desperation, Ellery and their friends are putting together a puzzle with a lot more pieces than Henry’s random shooting. Somebody in their city is preying on teenagers in a most insidious way, and nobody in their circle is going to let this stand.
Jackson has spent a year and a half trying to heal from physical and emotional wounds, and this case is going to make him look at every choice he’s made to survive. Ellery—and Ellery’s mother—will do anything to help him, but does Jackson finally have emotional defenses to fight his own demons while he’s slaying dragons for the family he’s found, or will he drown in his own remorse? Sometimes, when you’re a kid on the streets, living past tomorrow means choosing between the Devil and the Deep Blue Fish.