Ex-police officer Rachel Harris runs her first undercover operation as Field Office 19 investigates the activities of a couple of suspected arms dealers. When Field Office Leader Hannah is notified of a Prime Ministerial visit, she suspects an assassination plot, but will the team find the hitman in time?

Hackers utilise the state Emergency Communications System to broadcast what they claim to be footage of dead prison inmates. When MI5 denounces the broadcast as a hoax, terrorists set off a series of false alerts. Charlie suspects that the MI5 activity is related to the London bombing.

Jez and Kylie go undercover on a notorious housing estate to investigate a scam involving the sale of counterfeit radiation sickness medication. Police officers question Rob about the death of a fellow medical student at the time of the bombing. Rachel and Charlie try to uncover the identity of the double agent within MI5.

The horrific murder of two MI5 informants lead the team to discover a leak at a government-run Missing Person's Scheme. The race is on to find the source of the corruption and prevent the killings before they escalate. Rachel goes undercover to find further information on the cover-up and learns that a British scientist may have been wrongly imprisoned for his part.

A bank heist by eco terrorists, involving a 16-year-old suicide bomber, leads the team to uncover a secret deal between the British government and a Korean billionaire. Will the team be able to free the hostages and stop the terrorists from completing their deadly mission?

Charlie is convinced that Abid Malik can lead him to the traitor and prevent a second bomb attack. Vik and Rob are sent undercover to Camp Windsmere to break him out.