When a father and son are shot execution-style in broad daylight, the detectives immediately suspect a gangland hit and worry the violence could escalate.

When an eight-year-old boy finds his grandfather dead in a pub basement, he tells Rob that he was hit by a man with a baseball bat, but Vivienne doubts his story.

In exchange for turning a blind eye, Adrian gives Rob a tip about Sarah. Now believing that Sarah may still be alive, David and his team race to her find her.

While the team looks into the murder of a Portuguese au pair who was recently fired from her job, Vivienne and Rob start investigating David on the sly.

Construction workers find the remains of a young man who appears to have died more than a year ago, but his sister claims he's been sending her postcards all the while.