An abortion doctor is executed by an American pro-life terrorist; Mary Kane. An informant reveals that this is just the tip of the iceberg as Mary has 20 more bombs and plans on using them. To make matters worse she has started training more pro-life groups, within the UK.

Whilst on a routine check of the bugs in the Turkish Embassy, Zoe and all the other people in the embassy are taken hostage by terrorists who wish to negotiate the release of their parents from prison. If Zoe's cover as a PR consultant is blown she will almost certainly be killed. Things worsen when Harry realises that the attack on the embassy was all just a distraction from something much, much bigger.

Two former inmates are released from jail. One is an undercover MI5 asset and the other is an impressionable wannabe suicide bomber who has been radicalised in prison. They are set to launch an attack somewhere in London, but our team must time it right and step in at the eleventh hour to prevent a massive loss of life.

MI5's best officer, Peter Salter, seems to be joining the enemy. President Bush is scheduled to visit and it seems as though Salter is trying to stop the peace, is this all part of his mission or is he in fact a triple-agent?

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 UK vowing revenge for the death of his sons in a NATO bombing raid. Zoe is sent undercover to track him down, and stop any more deaths.

MI5's mainframe has been hacked into. But 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. Will they be able to stop the culprit before the inner sanctum is breached and every agents' identity revealed?

Far-right political party The British Way is threatening democracy so Adam and Fiona go undercover to infiltrate and destroy its campaign.

Disgraced MP Hampton Wilder has written memoirs with the power to destroy the government, what's more an old KGB agent is trying to smuggle illegal arms into and out of the country, besmirching the good name of the Prime Minister's right hand man.

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

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

A new series of strikes prompted by the unions has the team worried. And when news of a 'strike' by the army arise, Tom is sent undercover to investigate. Meanwhile Zoe takes charge back at the Grid, and is tasked with moving spent uranium cells across the country after rail strikes prevent it taking it's usual route. Will it get to Dover on time? Or will it fall into the wrong hands?

Section D is forced to welcome an FSB officer onto the Grid to help track down Aibek, a rogue nationalist from the ex-Soviet state of Azakstan. Aibek is in the UK to find the last known sample of the nerve agent 'Paroxocybin'. The chase is on, but will the team find a way to stop the nerve agent falling into the wrong hands without ruining Anglo-Russian relations? Meanwhile, Lucas's personal life takes a passionate turn.

A French scientist has gone renegade and taken a top secret weapon called Firestorm with him, which he is threatening to sell to the highest bidder. Now he has ended up in the UK, and MI5 is forced to work with French Intelligence. But the British want the technology. They have to steal the technology without the French finding out, using an agent that if caught has no affiliation to Five. But there is a burglary at Harry's flat which puts the operation in jeopardy. Or does it?

Tom is undercover with Customs, but when he goes off to phone in, the rest of the crew are murdered. A Colombian drugs cartel are suspected. Zoe and Tom are sent undercover to 'turn' the girlfriend of the head of the cartel. Tonight also sees the re-appearance of Tessa and she wants revenge on Harry and MI5. Will she endanger Tom and Zoe's life? Will the mole be found before it's too late? Or will Tessa get her revenge and allow someone to die?

Adam infiltrates a truck carrying illegal immigrants across Europe in order to stop a would-be terrorist.

The country reaches crisis point when energy supplies are threatened by an explosion at a gas processing plant. With reserves on the verge of running out, Britain is forced to turn to Tazbekstan for help. But in return for energy, the Tazbek Trade and Industry Secretary, Urazov, wants carte blanche to wipe out his enemies on British soil. Is this a price worth paying or can Section D get rid of Urazov in order to secure the deal?

The team has been left shocked by Lucas's betrayal, and with Harry Pearce on gardening leave, Section D has a new leader called Erin Watts. She has brought Calum Reed with her into the team. Harry Pearce manages to win his MI5 employment tribunal and is soon back on the Grid in the thick of the action. Secrets end up being discovered after Max Witt, a retired spy and Harry's colleague in Berlin during the Cold War, is discovered to have been murdered.

The pressure is on for Section D when a secret meeting of powerful tycoons is stormed by armed terrorists and eight of the world's richest men are taken captive. But this is no normal hostage situation - undercover at the time, Ros is one the hostages. As events spiral out of control, it looks like no one will make it out alive. Is this the end of the road for Ros?

Lucas's past comes back to haunt him when his former torturer Darshavin turns up with intelligence about a bomb in London. Harry fears Darshavin still has a psychological hold over Lucas, but Darshavin won't deal with anyone else. With innocent lives at risk Lucas must confront his demons for the sake of the nation, but can he overcome his nemesis in order to save the day or is the pressure too much to bear?

Harry is puzzled by the sudden death of CIA boss Samuel Walker. Harry is convinced that he did not commit suicide and when another CIA agent dies he begins to think that the deaths have something to do with the power meeting that is being held in Basel. Ros is surprised when her old mentor, Jack Coleville, contacts her and it soon becomes apparent he is involved in what has been going on.

When a highly skilled trio of Chinese agents arrive in London for 48 hours only, the team must find out why they are here. Ruth goes undercover in a major scientific research corporation where one Chinese scientist, Jiang, proves to be the ultimate prize. Beth activates an asset from the Chinese Security Services to be Section D's mole on the inside, but has she activated him too soon? Lucas makes a decision that could change his course forever.

The American president is on his way to London to chair top secret peace talks between Israel and Palestine, under the guise of his first state visit. Beth and Dimitri must keep their wits about them as undercover Home Office representatives, tasked with keeping the delegates apart until the talks. When a plot to kill the president is uncovered, they must also track down the assailant. The hotel is put in lockdown as a precaution, but are they locking the threat out? Or in?

Tom and Helen must go undercover and befriend the wife of a suspected hardcore racist in order to prevent a racewar. Meanwhile Zoe and Tessa learn that a boatload of refugees is due to dock at Dover in the next few days. Things worsen when the operatives realise the two things may be connected and their covers may be blown.

A British plane is thought to have been hijacked and taken to an American airstrip. Ros is captured by the Yalta organisation when the team shows up and they learn of an international cover-up.

As an Algerian extremist escapes his home detention, the team fears he may be plotting a terror attack on US businesses in the UK with the help of local Iranians. However, working with the Americans to stop the attack proves a trying task given their recently-deceitful behaviour.