A military jeep approaches Camp Windsmere Army Base, a high security detention facility. Within the base, a male nurse, David Younger, approaches the temporary morgue, enters, and starts filming bodies with a video camera.
Jez calls at the short stay accommodation centre in Sector 14. A girl, Kate Richards, answers, and lets him in. The couple make love. As Jez prepares to leave for work, Kate wonders what would happen if MI5 found out that he was sleeping with an informant.
Jez is late for work. It seems that Charlie has spent much of the night at the office. Sarah Yates, DFO, checks on Charlie before he takes up duty as interim team leader. She assures him that Central Command have the investigation into Hannah's death in hand, and that he and his team should concentrate on Field Office duties.
In his office, Charlie continues to try to view the content on the memory stick that Hannah left for him, but it is password-protected.
Jez and Vik are at Bridgewater University to see an informant. Every mobile phone on campus rings out as text messages are received, prompting the students to look at the public view screens located across the campus. The regular broadcast is interrupted, and all screens show footage from the mortuary at Windsmere. A caption reads "M.O.D. = Ministry of DEATH".
Charlie enters his own name as a password. It's accepted, and a file loads. The stick contains a video message from Hannah. Kylie interrupts with the news from Bridgewater. The alert system is supposed to be secure, and only MI5 agents have access. Windsmere has been a secret, but the story is now being carried across all media.
Tech think that someone hacked in using a wireless connection. CCTV reveals a suspect using a laptop near the transmitter. It's Kate. Rob sends the image to Jez and Vik.
Jez and Vik go to Kate's place, but she has cleared out. Jez confesses to Vik that he has been sleeping with her. He doesn't want to tell Charlie about their inappropriate relationship, as Charlie will report the breach to Yates. Vik is annoyed, but won't inform on him.
Jez has an address for Kate's parents, but it's a false lead. Kate is not her real name: she has stolen the identity of a girl missing since the bomb. Mr and Mrs Richards beg the officers to help find their daughter.
Saeed Khan, head of MI5, appears on television to confirm the existence of the detention facility at Windsmere. All detainees were being held lawfully under the terms of the Britannia Act. Yates is not happy about the security breach. Charlie assures her that Field Office 19 is on top of the situation. He thinks that the identity of the bodies in the video would lead them to the hackers. However, the MoD insists that the video is a fake.
At the transit accommodation camp, David and Kate watch the news broadcasts. He cannot believe that the government is dismissing the footage as a hoax. Kate expected this: the video was just the first step. They have to keep hurting the Government until it admits what it did.
Jez and Vik tell Charlie that the chief suspect is an MI5 informant. Kylie notes that MI5 phones and laptops use the same encryption protocols as the alert system. It will take tech a couple of days to change all access codes and prevent a further breach. Jez thinks Kate cloned his PDA.
DS Phillips calls on Rob about Julian Nelson, a fellow medical student who was working with Rob when the bomb went off. Julian's body was held in cold storage along with the victims of the attack. A post mortem has revealed that he died of an overdose. The police are not convinced that it was a suicide, and also want to speak to Emma Milton, Julian's girlfriend at the time.
Charlie asks Rachel to try to get the names of the Windsmere dead from her army contact.
Kate initiates an evacuation alert at Chapel Street railway station. The barriers are closed, and people get caught in a crush. The police and paramedics won't enter until MI5 confirm that it is a hoax. Charlie decides to treat the alert as genuine, until the bomb squad gives the all-clear. Three people die in the crush, and 14 are hospitalized. The media blame MI5 for issuing a false alert and causing the stampede.
Kate has previously been seen at Wood Road relocation centre. Rob goes to the centre, posing as a displaced person. He asks several residents if they recognise Kate from her photograph. He asks one resident, Billy, if he can help him get his hands on some fake ID.
Charlie joins Jez on the shooting range, and pressures him into confessing to his illicit relationship with Kate. Charlie says he will take the matter no further, but tells Jez he must never lie to him again. Jez shoots three times, but fails to hit the target.
Rachel meets Major Saunders at a car park in a CCTV black spot. He tells her that there was a riot at Windsmere. The army went in heavy, and there were three fatalities among the rioters. He is reluctant to give her the names of the dead, but gives in when she threatens to frame him for leaking the video.
Kylie accuses Rachel of fancying Charlie.
Rob's questions have made Billy suspicious, and he talks to David about it. That night, Rob is jumped by two men, but he overpowers them and escapes.
One of the men killed at Windsmere was Liam Daniels, arrested on suspicion of laundering money for a terrorist cell. Kate's real name is Laura Daniels, and she is Liams's sister.
Rob returns to the centre, accompanied by Jez, and they interrogate Billy. Threatened with being sent to Windsmere, he tells them that Laura was trying to obtain explosives, and tells them about David. At base, Kylie identifies David from his employment record at Wood Road centre. She confirms that he transferred to Windsmere two months ago, and obtains his address and photograph.
Jez and Rob go to the green residential sector, where they grab David. Jez threatens to shoot David, ho tells them that Laura is at Bridgewater.
The team mobilise the police and the bomb squad, and initiate a security alert at Bridgewater, but Laura counters it, declaring it a false alarm and blocking the team's access to the system.
Rob takes David to base, while Jez goes to the university to find Kate. He pulls a gun on her, but she threatens to detonate explosives she has placed on the site unless he lets her go. Jez places his gun on the floor. Laura apologizes for lying to him. Charlie, Kylie, Rachel and Vik arrive at the scene. Charlie shoots and kills Laura before she is able to detonate the explosives.
Back at the office, Charlie shows Rachel Hannah's video message.
"If you're watching this... I must be dead. Which probably means they got to me before I got to them. I believe there's a traitor within MI5. I don't know who, but I believe this person is directly responsible for the attack on London."