A rabid Pro-Life supporter, already sentenced to death for her actions in the United States, invades the UK with twenty bombs and it's up to MI-5 to stop her and find the location of her bombs.
Tom and Helen Flynn pose as a married couple to try and stop a man hellbent on starting a race riot.
Undercover agent Zoe is held captive when a Kurdish terrorist group gains control of the Turkish Embassy and demands the release of Kurdish prisoners.
A new agent, Peter Salter, is brought in with the mission to infiltrate a group of anarchists, but when he falls for one of the conspirators, he falls hard and ends up working on the opposite side of the law.
The MI-5 team have to deal with the aftermath when a jailed Parliamentarian's finger-pointing memoir leaks out.
The Grid, an Irish group, asks for an exchange with MI-5. In exchange for information about a potential terrorist bombing of a power station, the Grid asks to be unwatched for a period of thirty hours. Tom gets the okay without Harry's approval and the team has to stop a railway station bombing without drawing The Grid's leader's attention in doing so.
Tom's girlfriend and her daughter are threatened when they are trapped inside a sealed house with his laptop set to detonate. In separate bombing attacks, the Minister is killed and a top secret military base comes under fire. The team sends Zoe undercover to get to the Serbian terrorist Gradic's information source.
A young agent is outed and tortured during his infiltration of a mosque but discovers its sinister training of suicide bombers. MI-5 turns to an Algerian agent caught at Scotland Yard to re-infiltrate the mosque and prevent a bombing.