|Series 07, Episode 03|
|Air Date||28 October 2008|
|Next||A Chance for Peace|
Chief of Section D Ros Myers (Hermione Norris) introduces Lucas North (Richard Armitage) to one of Adam Carter's assets, Pakistani intelligence officer Marlin (Emilio Doorgasingh). Marlin has information about a planned attack by Al-Qaeda; a cell intends to create Internet chatter, followed by a dry run, after which they will commence a series of suicide attacks. The ringleader behind this is Nadif Abdelrashid (Ariyon Bakare) who was previously responsible for similar attacks in Turkey and Somalia. Ben Kaplan is in his first undercover operation disguised as a recent convert to Islam and becomes part of the cell. As part of his cover, Ben shares a flat with Jawad (Tariq Jordan), another member. However, over the course of the operation Ben becomes close to Jawad, which Ben's handler Lucas advises against, as Jawad is not an innocent.
When Malcolm Wynn-Jones (Hugh Simon) discovers the chatter, Ben relays to the team that the dry run will commence the following day. On the day, Ben finds that Abdelrashid intends to carry out the attack ahead of schedule and during the dry run after Ben, Jawad, and two other men are given bombs. Ben relays this message to Lucas. Ros dispatches CO19 to apprehend Abdelrachid in his office, who intends to remote detonate the bombs. Another CO19 squad, as well as Lucas and Jo Portman (Miranda Raison) follow the cell members to a street market, which they will use to maximise civilian casualties. Ben admits he is MI5 to Jawad, who runs in panic and attempts to manually detonate his bomb; this results in getting gunned down by CO19 officers, much to Ben's dismay. After stopping another two bombs, Jawad's mobile phone rings, revealing Abdelrashid is not the "Mr. Big"; it is Marlin. He remote detonates the last bomb, killing the terrorist and the two CO19 officers holding him.
Although one bomb did detonate, Harry Pearce (Peter Firth) views the operation a success, as the other three did not, and no civilians were killed. Ben tells Lucas he was right about Jawad; he chose to become a bomber over seeing his family. Lucas receives a call from Marlin, who asks to meet with him. During the confrontation, Marlin admits he was forced to become Mr. Big when terrorists kidnapped his family. Now knowing he has failed, he commits suicide.
In a subplot, rainwater falls onto Lucas's face, which triggers a flashback where he was tortured by FSB interrogators during his eight year imprisonment in Russia. The interrogators question him on "Sugarhorse." Lucas relays this to Harry, who claims not knowing what Sugarhorse is. However, he later visits a retired spycatcher Bernard Qualtrough (Richard Johnson) believing there is high level mole within MI5. He only reveals that Sugarhorse is MI5's "best kept secret" that only five people, including Richard Dolby (Robert East), the Director General, and himself, know the details of. Harry later returns to Qualtrough's bookstore to find out who the mole might be, starting by looking into Dolby's file.