Detective John Hollis has spent the past twenty years entrenched in Robbery and Homicide's gritty underworld, chasing perpetrators and bringing them to justice. Yet, for all his experience, nothing could have prepared him for his current investigation: finding the person responsible for his son's murder.

In this second installment, John is pulled back to Los Angeles after Jacob's body washes ashore, tragically ending his two-year disappearance. Following a meeting with the unit's captain, he is reinstated to his former rank within the LAPD, joining a squad of new and old faces, including his former partner. Together, they waste no time connecting Jacob's death to the murders of two other teenaged boys after they discover a mysterious name neatly buried in their case files.

But as the investigation progresses, a key finding reveals Jacob's connection to a widely known narcotics distributor, and it soon becomes clear that what binds the three young men is not a name at all, but a code. The discovery, however, raises eyebrows when the thin blue line is called to task, eventually exposing profound fractures, secrets and other hidden betrayals that, for John, strike unexpectedly close to home.