'Traitor's Gate', written by Howard Brenton, directed by Rob Bailey (BBC1, tx. 4/6/2002)

On surveillance duty during an anti-globalisation march in London, Danny and Zoe recognise a man stopped by the police as Peter Salter, one of their field agents. Although he is not on their list of agents involved in the event, they get him released. Tom is meant to be running Salter, but has not been told of the operation. Harry tells him that Salter is working on a joint operation for both MI5 and MI6 to catch Istvan Vogel, who is planning to undermine the upcoming visit of US President Bush.

Harry and Tom meet with MI6 chief Jools Siviter and, using surveillance equipment, they watch Salter as he talks to group member Andrea. Salter tells her that he used to be an MI5 agent but has gone over to her side and wants to help Vogel. Concerned by the fact that he has blown his cover, Tom decides to remove Salter from the operation. Salter tells him that he has fallen in love with Andrea and begs for a few extra hours to settle things with her. As Salter was his original mentor in the Service, Tom gives him until morning.

Tom finally has to admit to his girlfriend Ellie that he is really a secret agent when she discovers he is nursing a gunshot wound from a recent mission. She is angry about his deceit.

Salter gives MI5 surveillance the slip and is taken to meet Vogel. He scoffs at their disruption plans and tells them that he knows how to penetrate London air traffic control. Harry instructs all his agents to look for any information on Vogel's activities. Zoe is sent to meet one of Tessa's informants and discovers that Tessa has been running phantom agents and pocketing their fees.

Together with Andrea and Vogel, Salter breaks in to one of the computers on a University campus but is arrested by the police after the others get away. Tom tells him that they caught Andrea but Salter sees through the lie. Salter immobilises Tom and then commits suicide rather than reveal the details of the mission and Andrea's whereabouts.

Danny realises that Salter has broken in to computers controlling the maps of Air Traffic Control and has reset them in such a way that President Bush's plane will crash on its way to the UK. He averts disaster at the last minute, diverting the plane.