Lucas goes undercover aboard a merchant ship on which a known member of Al Qaeda is traveling to the UK. The ship is soon taken over by terrorists and it becomes clear that they are planning a coordinated attack of some sort. Lucas isn't the only MI-5 agent on board but Lucas' main help in the operation comes from a private security officer, Beth Bailey. Back in London, Harry Pierce has a particularly difficult encounter with the former Home Secretary, Nicholas Blake. Harry decides that it's time to retire but is again faced with making life and death decisions. Written by garykmcd

When MI-5 learns that Nigerian assassins are out to kill British oil man Robert Westhouse, they send in a team to protect him. Westhouse owns a large piece of Nigerian oil production which is vital to the British economy. Beth Bailey attends a meeting at his offices with a group of others but on the way up in the lift, the car stops and gunmen open fire in an attempt to kill everyone inside. Beth survives as does Dubai-based business man Jacob Chapman. Harry and Lucas assume one of the men in the car was the assassin but it's not quite as simple as that. Meanwhile, Lucas delves into the briefcase of material he was given by a former acquaintance and visits someone from his past life. It turns out that Lucas isn't the only MI-5 officer with secrets from their past however. Written by garykmcd

The Home Secretary orders Harry to support a Russian plan to stop the Azakstan Freedom Front from obtaining a deadly biological weapon that was supposed to have been destroyed in the 1960s. The AFF supports independence from Russia and Lucas North works with the Russian security service, the FSB, in stopping them, though he doesn't necessarily agree with their shoot first approach to dealing with terrorists. One of the terrorists, Azis Aibek, manages to escape and make his way to London to see if he can get the British sample of the WMD. In an unprecedented move, the Home Secretary orders Harry to let and FSB officer onto the grid as they hunt Aibek down. Lucas meanwhile contacts Maya and promises to tell her why he never contacted her. Written by garykmcd

MI-5 is on alert when a report from the UK Border Agency reveals that a highly sophisticated Chinese hit team has entered the country. The CIA station chief says they know of no reason why the team might be in the UK and MI-5 determines that their interest is likely a British-designed water desalination system. Beth has been working on turning a Chinese Embassy employee but her rushed effort leads to failure, at least initially. Ruth Evershed goes into the company undercover only to find that the CIA is involved and protecting the scientist who developed the new desalination process. When the Chinese station chief threaten to set off a bomb n central London, Harry must decide whether to let them have the scientist or face down their threat. Lucas meanwhile struggles to keep his past a secret. Written by garykmcd

London is to host secret Middle East peace talks chaired by the President of the United States. The chief Israeli negotiator is Levi Cohen who is accompanied by his estranged daughter Anna. They have not spoken for many years dating back to when Levi refused to negotiate with terrorists who had taken her captive. MI-5 is in charge of security for the talks, which have been assigned the code name Horizon. Dimitri and Beth go in masquerading as Home Office employees, but their ruse doesn't last long. When a journalist gets hold of the story, MI-5 wants to know who her source is. They focus on Muatt Hutri, a Lebanese terrorist who has just arrived in London. It's not at all straightforward as it seems however. Meanwhile, Vaughn Edwards is increasing pressure on Lucas to get him a copy of the Albany file. Written by garykmcd

The CIA provides MI-5 with what is supposed to be a hacker-proof computer system, Cybershell, but Tariq realizes that the Grid has been hacked into already. They are being watched and the hackers have access to everything. Once connected to the American system, the hackers will have access to that information as well. Lucas is supposed to collect the American crypto-officer and deliver her to Thames House but he receives a final warning from Vaughn Edwards to deliver the Albany file or Maya will fall victim to him. Lucas turns to a former colleague, Malcolm Wynn-Jones, who he believes knows how to retrieve Albany. Back at Thames House, Harry and the others are trapped when the hackers lock them in and shut down the power. Written by garykmcd

Harry takes Lucas along to meet a onetime informer who says he has information on the bombing of a British Embassy some 15 years ago. That case is one Harry would very like to solve. The informant turns out to be none other that Vaughn Edwards who is offering Harry the same information he's been using to blackmail Lucas. The information Lucas delivered to him previously was useless and Edwards now has only a few hours to finalize the deal. By now, Harry and Ruth realize that Lucas is in big trouble and take him into custody. There he reveals his true identity. Ruth meanwhile stumbles onto an assassination plot when a local council worker brings her information. She looks into it only to be taken prisoner by the assassin. Written by garykmcd

Lucas is on the run and has taken Ruth prisoner. He gives Harry a simple choice: the Albany file for Ruth's life. Harry is determined not to let Ruth down again and decides to make the swap in the hopes that they can subsequently stop Lucas before he delivers the file to the purchasers. Harry approaches an ex-MI5 Internal Affairs officer, Alec White, to help them track Lucas. The nature of the super-secret Albany file is revealed as are the final pieces of Lucas' background. Not everyone will survive and for those who remain, the future is decidedly unclear. Written by garykmcd