Andy McNally’s first shift on the job turns into mayhem when shots are fired in a downtown rooming house. In the midst of the chaos, Andy triumphantly makes her first big arrest – a suspected drug dealer – who turns out to be Sam Swarek, an undercover officer from her own division. She makes up for her grave mistake by going face to face with a dangerous gunman who already has one man’s blood on his hands.

A home invasion at an upscale address leads to a massive first response call that brings out the training officers in full force. After the scene is cleared, Andy and Traci remain behind with the terrified homeowner. When Traci is called away to deal with an emergency with her son, Andy is left alone to face the armed thief who is still prowling around the house.

A severe heat wave wreaks havoc on the city, forcing the rookies to work around the clock to keep the peace. In the midst of the chaos, Andy discovers that a serial rapist may have resurfaced to prey on vulnerable teenage girls. And when the extreme temperature precipitates a citywide blackout, Andy finds she’s cut off from all backup and must take.

The torching of a Laundromat is the latest in a series of arsons which the 15th Division must work. The list of suspects is long so Chris and Gail take to the streets while Traci interrogates a person found at the scene. Andy is left to deal with the widow who insists on entering the burnt-out building which ends with the two of them trapped inside.

Indications are that the East Jameson gang was involved in the murder of a police informant, so solving the case will be difficult. The pressure is on when Superintendent Elaine Peck sets up at the station. Elsewhere, Andy is paired with Detective Rosati who unintentionally makes Andy privy to a secret that involves Luke. Stressed out with her mother at the station, Gail is tasked with protecting an eight-year-old boy who's the only witness to the crime.

A violent pedophile escapes during an emergency hospital visit and abducts a girl; Andy faces a serious decision; Chris considers a transfer.

During a routine traffic stop, Gail and Andy find a teenage boy bound and gagged in the trunk of a car; Oliver, Chris and Swarek track a gunman.

When Andy and Chloe respond to a routine 911 call, they are blindsided by an unseen shooter out for revenge.

In the aftermath of the night's traumatic events, Andy and Dov try to pull themselves together at an all-night diner, but are caught off-duty and off-guard in a volatile diner hold-up. Meanwhile, the weary officers at 15 Division struggle to contain the evening's collateral damage under the watchful eye of a tough new Inspector.

It's a day of firsts as Oliver gets promoted to Acting Staff Sergeant and Andy is tasked with training 15 Division's newest rookie, Duncan Moore. But when Andy and Duncan respond to a messy homicide at a pawnshop, it's clear this rookie is going to give Andy the challenge of a lifetime.

Andy and Sam are shocked to learn that Oliver is the prime suspect in IA’s corruption investigation into 15 Division. What’s worse, they only have until end of day today to find Chris Klem – the missing explosives-dealer – and clear Oliver’s name before he takes the fall.