The series picks up exactly where we left it. With Tom's family trapped in his house with a bomb and nothing Tom or the other Spooks can do but watch on. There is a huge explosion and the credits begin.

However there is no time to focus on these events as a Serbian Warlord has been seen entering the U.K. vowing revenge for the passing of his sons in a N.A.T.O. bombing raid. Zoe is sent undercover to track him down, and prevent any further passings.

A fellow agent informs Tom that young men attending a mosque in Birmingham are being trained as sleeping bombers. They need to find a suitable agent to penetrate the mosque.

MI5's mainframe has been hacked into. Tom and his team think they have found a lead in the form of an I.T. teacher, so Zoe is sent undercover to get close to him and find out his secrets before the inner sanctum is breached and the identity of every agent is revealed.

After stealing a large amount of money from a bank a man is found crucified on the moors. The Treasury calls in the team to investigate but when Harry decides to take the mission further Danny's life is put in danger.

Tom's skills as leader are tested to their extremes when they take part in an Extreme Emergency Response Initiative Exercise (EERIE) to test their response to nuclear, chemical or biological act in central London, but when the power in the grid is cut and Harry starts to feel ill, they soon begin to suspect it is for real.

The U.S. President makes an unexpected stop in London. Tom and his team are forced to work with the CIA. A power struggle between the two secret organisations begins but will they stop fighting before a terrible mistake is made? And will Tom's ex-girlfriend leave well alone or will she have to be taught a lesson?

A renegade scientist has developed Firestorm, a top secret weapons system, for the French military, but is now threatening to sell it to the highest bidder. The British want the technology, and MI5 are tasked with stealing it without alerting the French intelligence service. A buglary at Harry's flat seems to put the operation in jeopardy.

A new series of strikes has the team worried. When the team gets news of a "strike" by the army, Tom is sent undercover to investigate. Meanwhile, rail strikes disrupt the transportation of spent uranium cells, and Zoe has to ensure that it reaches its destination.

A Colombian drugs cartel is implicated in the cuddle of a team from Customs and Excise. Zoe and Tom are sent undercover to "turn" the girlfriend of the head of the cartel. Tessa, still nursing a grudge against Harry and MI5, reappears, and her interference may jeopardize the operation.

Tom ignores Harry's demands to end his relationship with CIA officer Christine Dale. Christine hands Tom a secure communication which she has accidentally received from high up in the CIA. It says that an American assassin has come to the UK for a hit and that the CIA are going to take him out, without informing MI5 or any of the security services. Tom can't tell Harry what he knows so enlists Danny and Zoe to help him, but things start to go terribly wrong.