The episode focuses on MI5 and 6's efforts in taking down a terrorist cell before they can succeed in attacking 43rd President of the United States George W. Bush.
The episode guest stars Anthony Head and Hugh Laurie, who play their respective characters Peter Salter and Jools Siviter.
After getting shot during the Turkish consulate raid in the previous episode,[2] Tom Quinn (Matthew Macfadyen) is on sick leave until he recovers.
Over the course of the episode, Ellie threatens to leave Tom unless he also explains his job to her daughter, Maisie (Heather Cave).
Danny (David Oyelowo) and Zoe (Keeley Hawes) observe an anti-globalisation rally before Bush's visit, where a riot ensues led by a man in a flaming helmet, who spots the two and flees with a young woman, Andrea Chambers.
When they are surrounded by riot police, the man reveals himself as Peter Salter (Anthony Head), a legendary MI5 officer who recruited Tom.
In the end when Ellie asks Tom about his day, he replies; "a man, who believed in a cause, killed himself for love, totally pointless."
The location where Tom and Salter meet in the middle of the episode was to be set in the Millennium Dome; this would later change to North Greenwich tube station.
The introduction of Tessa being corrupt by running phantom agents was allegedly based on real life situations.
[5] Hugh Laurie was cast as Jools Siviter; the character was created because of bringing in a lighter element to a generally serious series.
[5] The scene where Tessa explains her treachery to Zoe was filmed at the women's public swimming baths of Hampstead Heath.
[5] After its original airing on BBC One, "Traitor's Gate" was seen by 5.99 million viewers in the UK, making Spooks the seventeenth most viewed broadcast on BBC One, and the thirty-second most viewed broadcast in total during the week; the episode became the lowest rated episode in the entire first series.