Josh rescues two children but then risks his career and puts the Tactical Response team in jeopardy when he takes his rage out on their father. The team is rattled by the unexpected arrival of new Inspector, Kerry Vincent. Although the team disapproves of Josh's actions they close ranks around him, forcing Kerry to begin her own investigation.

The end of a long night shift finds Lawson, Grace and Dom in pursuit of a car driven by two lovestruck teenagers who have panicked after an attempted robbery turned to murder. When the teenagers are chased to a rooftop and threaten suicide, Grace steps up as chief negotiator and is forced to face the consequences of her inexperience. Michael, new to Tactical Response, encounters first-hand the tough reality of his job.

A gunman shoots Stella, who is saved by her bulletproof vest. Lawson realises the man is trying to commit suicide-by-cop. Putting his own life on the line in a face-to-face negotiation Lawson recognizes the gunman as his former mentor. While Stella confronts her brush with death, Lawson is forced to act against his beliefs and shoots, killing someone he knew well.

The Tactical Response Unit pursues a criminal who assaults Grace while escaping. Josh allows himself to be taken hostage. Preferring death to capture, the criminal forces Josh into a sadistic game of Russian roulette. Despite his ordeal Josh chooses to save the man's life and convinces him to surrender. Grace's injury causes her husband Connor to question her choice of careers.

The Tactical Response team faces a dangerous situation when an armed robbery turns into a siege with hostages in a suburban pub. Lawson and Josh surprise the robbers and are shot at when they arrive at the pub so they send Dom in as an undercover ambulance officer. Kerry and Lawson begin working well together for the first time.

Grace, Josh and Dom are investigating an activist attack at a research laboratory when firebombs explode, putting their lives at risk. Stella discovers that her brother, who is also a cop, is corrupt and reluctantly chooses to protect him. Michael faces his own mortality after being bitten by a monkey infected with a fatal disease.