:Episode 1 - Communication:

A ship changes course for Southampton after a bloody battle on board between gangs of Turks and Frenchmen, leaving the skipper Willem not knowing who is in charge.

That same night, Jamie Dow and Captain Caroline Walshe of the SAS enjoy a night of passion, but they are spotted by Red Troop's leader Sergeant Henno Garvie.

Henno welcomes back Pete Twamley after four months on the critical list, but he's angry to be left behind doing paperwork when the team are called for surveillance duties in Southampton on the MV Dowager Joan.

Attractive MI5 operative Pru Banks explains that they want the SAS to gain access to the ship secretly to install a high-grade tracker. But they know little about the crew and why they are under suspicion.

Henno warns Caroline to end her relationship with Jamie, but when Jamie learns their secret is out, he ends it first. Meanwhile, Jem Poynton winds up tetchy new recruit Louis Hoffman as they set up an observation point.

Back at base, Twamley has a horrific nightmare and almost strangles his wife, but he denies suffering from flashbacks or post-traumatic stress. He just wants his job back.

Louis spreads gossip about Jamie and Caroline's relationship as Henno and Jamie swim underwater to board the ship. They plant the tracker successfully but are trapped when two men come into the cabin.

While Henno looks for a new hiding place, Jamie spots a room full of prisoners, then is surprised by a skilful attack from a Frenchman. Henno comes to his aid and they kill the man, but a communication breakdown prevents them from reporting back to base. Inside a cold store, they hear the ship's engines start - then spot another dead body and realise this is not an exercise.

The crew discover the dead Frenchman and search for his killer as Caroline boards the ship, posing as a customs officer. Jem spots a gun and tells Louis to lob a grenade, just as commander Aidan Dempsey gets the news that the men are French Special Forces. But it's too late - a tremendous gun battle is underway with Red Troop in the firing line...