Johnny Marks: You know the part I'm going to miss most? The part where you have to explain away the loss of fifteen million pounds.
Harry Pearce: You and I both know you are not just going to walk away from this.
Johnny: How much are three thousand agents' names worth? Are you prepared to sacrifice all those people just for me? I walk, you get the names.
Harry: How do I know that I can trust you?
Johnny: Because I have never broken my word.
— "One Last Dance"
The MI-5 officers of Section D constantly struggle to maintain the peace within the United Kingdom from terrorist threats. These elusive and proficient criminals are the ones who make their jobs much more difficult.
All spoilers are unmarked. You Have Been Warned!
Series Wide
- Series 1 & 2: Tessa Phillips is an MI-5 agent who's secretly stealing money from the government. Using fabricated confidential informants, Tessa repeatedly fools MI-5 into paying the informants small sums of cash so she could later launder the money into her own bank account. After Zoe Reynolds uncovers the truth about Tessa, Tessa simply bribes Zoe with ten thousand pounds to keep her silent. Later on, after Tessa is fired by Harry Pearce for her actions, she seeks revenge against him by posing as Harry's boss and fooling Sam Buxton into delivering confidential information to her in regards to the Chala Cartel. After seemingly agreeing to help MI-5, Tessa later exposes one of their informants and has her employers assassinate the cartel leader, fleeing the country afterwards to avoid prosecution from Harry.
- Series 6 & 7: Connie James is an MI-5 agent secretly working as a spy for Russia. Feeling the world was becoming unbalanced after the Cold War, Connie assisted the Russian government for several years by helping create "Tiresias," a Russian operation where hundreds of deep cover agents were planted inside Britain, selling confidential information that got agents killed, and even having Lucas North arrested and tortured for eight years. When Harry Pearce and other Section D officers learn there's a spy in the British government, Connie offers to help them, all while diverting suspicion from herself and framing Harry later on. After having her cover blown and learning a sleeper agent intends to set off a nuclear bomb, Connie offers to defuse the bomb and give up all the Tiresias operatives to Section D in exchange for full immunity. Even after triggering the bomb's failsafe, Connie dismantles its core anyway so it won't become nuclear, knowing full well it will explode once she finishes.
- Series 9: Vaughn Edwards is a mercenary and master deceiver. Seeking out a partner to help him with his schemes, Vaughn recruited John Bateman and used him to conduct unofficial operations for the British government. After the two successfully bomb a British embassy, Vaughn helps John kill Lucas North, a soon-to-be MI-5 agent, and steal his identity. Fifteen years later, Vaughn seeks out John in London and blackmails him into stealing a government file known as Albany or else he'll expose his true identity to MI-5 and his former lover, Maya Lahan. After John repeatedly fails, Vaughn goes to Harry Pearce directly and threatens to reveal who was behind the embassy bombing. When John mortally wounds Vaughn to silence him for good, Vaughn uses his dying breath to tell John that he's nothing more than a killer pretending to be a hero.
Single Episodes
- "One Last Dance": Johnny Marks is a former MI-5 asset who betrayed his employers and became a freelancer. After faking his death in a car bomb, Johnny resurfaced in London several years later to pull off a heist. Using Kurdish rebels at his disposal, Johnny had them take over a Turkish consulate, distracting the authorities so he would be able to steal $15 million from a bank. He also acquired the identities of thousands of undercover MI-5 and MI-6 officers as leverage. Once Johnny has the money, he leaves the rebels to be apprehended while he escapes. Even when Harry Pearce manages to confront Johnny in person, Johnny threatens to expose the agents' identities, forcing Harry to let Johnny go free.
- "Smoke and Mirrors" & "Project Friendly Fire": Herman and Carmen Joyce are an ex-CIA couple with a grudge against Tom Quinn. After their daughter, Lisa, is institutionalized due to a mental breakdown during an MI-5 operation Tom recruited her for, Carmen opts to ruin Tom's life. She and Herman stage a car crash and fake Herman's death before spending years plotting to frame Tom for an assassination. Herman murders an assassin in the Witness Protection program before traveling to London and fabricating documents to make it look like Tom's a traitor. After luring Tom, Danny, and Zoe to a farm for interrogation, Herman frees Tom to further implicate him, before drugging him and placing his fingerprints on a sniper rifle used to assassinate the Chief of Defence Staff. When Tom, now a fugitive, subdues Herman and tries to get him to turn himself in, Herman refuses, telling Tom he'd rather die knowing he destroyed his life. Later on, after MI-5 corners Carmen in a safe house, Carmen admits to everything she and her husband planned before killing herself, satisfied that her and Herman's plans succeeded.
- "Road Trip": Ali Mohammed Yazdi is an assassin working for the the Al-Kahf terrorist cell. After receiving a contract to murder Middle-Eastern diplomat Prince Hakim, Yazdi uses his connections with a smuggling operation to sneak into Britain. Upon being discovered by Adam Carter and offered a deal to become a double agent, Yazdi begrudgingly takes the deal to fool MI-5 into believing he's turned. While working for MI-5, Yazdi gives up the name of one of his contacts and surreptitiously forces him to give up Prince Hakim's name, all while pretending that the Al-Kahf are planning another terrorist attack to divert MI-5's suspicion. Once MI-5 brings Prince Hakim in for questioning and put him in the same room as Yazdi, Yazdi swiftly kills the prince using nothing but his own glasses.
- "Diana": Angela Wells is a former MI-5 agent and covert operative working for a group of government conspirators. After her fiancé, Peter Haigh, commits suicide when no one believed that MI-5 had Princess Diana murdered, Angela decided to prove his theory by force. Armed with explosives, Angela entered Thames House and forced various MI-5 operatives to prove Diana was murdered, or else she'll blow the whole building. After Ruth Evershed convinces Angela to surrender, Angela uses her grief over Peter to cajole Harry Pearce into letting her go, only to steal a document that left the Royal Family's security vulnerable. Angela fools MI-5 into evacuating the Royal Family into a bunker she installed a bomb inside of and nearly kills them. When her plans fail, she retaliates by attacking Harry and Adam Carter with a sniper rifle before warning them that more attacks with ensue in the future.
- "The Criminal": Richard Dempsey is a former MI-6 agent believed to have turned traitor to the Balkans. In truth, Dempsey has been working undercover with Serbian war criminals General Marko Tezlia and Colonel Niko Grecic whilst also feeding crucial information back to England for his superiors' benefits. In order to preserve his cover, Dempsey willingly stopped Adam Carter from assassinating Tezlia, which led to Adam being tortured and almost killed. Several years later, after finding out he's being framed for the deaths of key witnesses testifying against Tezlia, Dempsey goes to Hungary and kills two hitmen sent to murder him before sneaking back into London and meeting Adam in private. Using clues his handler left behind, Dempsey successfully convinces Adam to help him find information that will exonerate him and implicate his superiors who betrayed him. After Grecic testifies against Tezlia and gets him arrested, Dempsey tracks down Grecic months later and assassinates him as punishment for the crimes he committed.
Film
- The Greater Good (2015): Adem Qasim is the charismatic leader of a Middle-Eastern terrorist cell opting to dismantle the British government. After Qasim is broken out of a prison transport, he resumes his plans to attack the government while also figuring out that Erin Watts was working undercover in his organization. After mortally wounding Erin and forcing Harry Pearce to execute her, he agrees to help Harry expose a traitor in MI-5 in exchange for being reunited with his wife. Qasim also has a suicide bomber kill the chairman of the Joint Intelligence Committee and releases a live video requesting for the public to stand up against their oppressors. Upon learning that his wife was killed, Qasim accepts Harry's second offer to infiltrate MI-5 headquarters so long as he calls off his impending bombing on Oxford Circus. Qasim gives up his own men planning the bombing while simultaneously attacking MI-5 headquarters, successfully killing several MI-5 personnel during his siege.
