Code Blue by Alisa Shaw

When Boston Homicide Detective Sean Malone returns home to find his wife murdered and his children missing, he discovers a familiar calling card scrawled in blood: a Celtic knot tied to a serial killer he's been hunting for years.

But the symbol is only the surface. A voice from Sean's past—Irish mob enforcer Seamus Byrne—forces a darker truth into the light: fifteen years ago, Sean helped shut down a cold case that should've stayed dead. Now a killer is tearing it open, one body at a time.

As the investigation pulls him deeper into South Boston's criminal undercurrent, Sean realizes the line between the mob and the institution he serves is thinner than he ever admitted. With his partner Detective Carla Reyes watching his every move and federal pressure closing in, he's running out of time—and out of places to hide.

The question is no longer who took his family. It's what Sean Malone did that made it possible.

Code Blue is a gripping crime thriller for fans of Dennis Lehane, Michael Connelly, and Lisa Gardner.