Tense drama series about the different challenges faced by the British Security Service as they work against the clock to safeguard the nation. The title is a popular colloquialism for spies, and the series follows the work of a group of MI5 officers based at the service's Thames House headquarters, in a highly secure suite of offices known as The Grid.
| Title | Air Date | Duration | ||
|---|---|---|---|---|
| Season 1 | Episode 1 | Thou Shalt Not Kill | 2002-05-13 | 60 min |
| Season 1 | Episode 2 | Looking After Our Own | 2002-05-20 | 60 min |
| Season 1 | Episode 3 | One Last Dance | 2002-05-27 | 60 min |
| Season 1 | Episode 4 | Traitor's Gate | 2002-06-04 | 60 min |
| Season 1 | Episode 5 | The Rose Bed Memoirs | 2002-06-10 | 60 min |
| Season 1 | Episode 6 | The Lesser of Two Evils | 2002-06-17 | 60 min |
| Season 2 | Episode 1 | Legitimate Targets | 2003-06-02 | 60 min |
| Season 2 | Episode 2 | The Nest of Angels | 2003-06-09 | 60 min |
| Season 2 | Episode 3 | Spiders | 2003-06-16 | 60 min |
| Season 2 | Episode 4 | Blood and Money | 2003-06-23 | 60 min |
| Season 2 | Episode 5 | I Spy Apocalypse | 2003-07-07 | 60 min |
| Season 2 | Episode 6 | Without Incident | 2003-07-14 | 60 min |
| Season 2 | Episode 7 | Cleanskin | 2003-07-21 | 60 min |
| Season 2 | Episode 8 | Strike Force | 2003-07-28 | 60 min |
| Season 2 | Episode 9 | The Seventh Division | 2003-08-04 | 60 min |
| Season 2 | Episode 10 | Smoke and Mirrors | 2003-08-11 | 60 min |
| Season 3 | Episode 1 | Project Friendly Fire | 2004-10-11 | 60 min |
| Season 3 | Episode 2 | The Sleeper | 2004-10-18 | 60 min |
| Season 3 | Episode 3 | Who Guards the Guards? | 2004-10-25 | 60 min |
| Season 3 | Episode 4 | A Prayer for My Daughter | 2004-11-01 | 60 min |
| Season 3 | Episode 5 | Love and Death | 2004-11-08 | 60 min |
| Season 3 | Episode 6 | Persephone | 2004-11-15 | 60 min |
| Season 3 | Episode 7 | Outsiders | 2004-11-22 | 60 min |
| Season 3 | Episode 8 | Celebrity | 2004-11-29 | 60 min |
| Season 3 | Episode 9 | Frequently Asked Questions | 2004-12-06 | 60 min |
| Season 3 | Episode 10 | The Suffering of Strangers | 2004-12-13 | 60 min |
| Season 4 | Episode 1 | The Special (Part 1) | 2005-09-12 | 60 min |
| Season 4 | Episode 2 | The Special (Part 2) | 2005-09-13 | 60 min |
| Season 4 | Episode 3 | Divided They Fall | 2005-09-22 | 60 min |
| Season 4 | Episode 4 | Road Trip | 2005-09-29 | 60 min |
| Season 4 | Episode 5 | The Book | 2005-10-06 | 60 min |
| Season 4 | Episode 6 | The Innocent | 2005-10-13 | 60 min |
| Season 4 | Episode 7 | Syria | 2005-10-20 | 60 min |
| Season 4 | Episode 8 | The Russian | 2005-10-27 | 60 min |
| Season 4 | Episode 9 | The Sting | 2005-11-03 | 60 min |
| Season 4 | Episode 10 | Diana | 2005-11-10 | 60 min |
| Season 5 | Episode 1 | Gas and Oil (Part 1) | 2006-09-17 | 60 min |
| Season 5 | Episode 2 | Gas and Oil (Part 2) | 2006-09-17 | 60 min |
| Season 5 | Episode 3 | The Cell | 2006-09-18 | 60 min |
| Season 5 | Episode 4 | World Trade | 2006-09-25 | 60 min |
| Season 5 | Episode 5 | The Message | 2006-10-02 | 60 min |
| Season 5 | Episode 6 | Hostage Takers (Part 1) | 2006-10-09 | 60 min |
| Season 5 | Episode 7 | Hostage Takers (Part 2) | 2006-10-16 | 60 min |
| Season 5 | Episode 8 | Agenda | 2006-10-23 | 60 min |
| Season 5 | Episode 9 | The Criminal | 2006-10-30 | 60 min |
| Season 5 | Episode 10 | Aftermath | 2006-11-13 | 60 min |
| Season 6 | Episode 1 | The Virus (Part 1) | 2007-10-16 | 60 min |
| Season 6 | Episode 2 | The Virus (Part 2) | 2007-10-16 | 60 min |
| Season 6 | Episode 3 | The Kidnap | 2007-10-23 | 60 min |
| Season 6 | Episode 4 | The Extremist | 2007-10-30 | 60 min |
| Season 6 | Episode 5 | The Deal | 2007-11-06 | 60 min |
| Season 6 | Episode 6 | The Courier | 2007-11-13 | 60 min |
| Season 6 | Episode 7 | The Broadcast | 2007-11-20 | 60 min |
| Season 6 | Episode 8 | Infiltration | 2007-11-27 | 60 min |
| Season 6 | Episode 9 | Isolated | 2007-12-04 | 60 min |
| Season 6 | Episode 10 | The School | 2007-12-18 | 60 min |
| Season 7 | Episode 1 | New Allegiances | 2008-10-27 | 60 min |
| Season 7 | Episode 2 | Split Loyalties | 2008-10-27 | 60 min |
| Season 7 | Episode 3 | The Tip-Off | 2008-10-28 | 60 min |
| Season 7 | Episode 4 | A Chance for Peace | 2008-11-03 | 60 min |
| Season 7 | Episode 5 | On the Brink | 2008-11-10 | 60 min |
| Season 7 | Episode 6 | Accidental Discovery | 2008-11-17 | 60 min |
| Season 7 | Episode 7 | The Mole | 2008-11-24 | 60 min |
| Season 7 | Episode 8 | Nuclear Strike | 2008-12-08 | 60 min |
| Season 8 | Episode 1 | Episode 1 | 2009-11-04 | 60 min |
| Season 8 | Episode 2 | Episode 2 | 2009-11-06 | 60 min |
| Season 8 | Episode 3 | Episode 3 | 2009-11-13 | 60 min |
| Season 8 | Episode 4 | Episode 4 | 2009-11-20 | 60 min |
| Season 8 | Episode 5 | Episode 5 | 2009-11-27 | 60 min |
| Season 8 | Episode 6 | Episode 6 | 2009-12-04 | 60 min |
| Season 8 | Episode 7 | Episode 7 | 2009-12-11 | 60 min |
| Season 8 | Episode 8 | Episode 8 | 2009-12-23 | 60 min |
| Season 9 | Episode 1 | Episode 1 | 2010-09-20 | 60 min |
| Season 9 | Episode 2 | Episode 2 | 2010-09-27 | 60 min |
| Season 9 | Episode 3 | Episode 3 | 2010-10-04 | 60 min |
| Season 9 | Episode 4 | Episode 4 | 2010-10-11 | 60 min |
| Season 9 | Episode 5 | Episode 5 | 2010-10-18 | 60 min |
| Season 9 | Episode 6 | Episode 6 | 2010-10-25 | 60 min |
| Season 9 | Episode 7 | Episode 7 | 2010-11-01 | 60 min |
| Season 9 | Episode 8 | Episode 8 | 2010-11-08 | 60 min |
| Season 10 | Episode 1 | Episode 1 | 2011-09-18 | 60 min |
| Season 10 | Episode 2 | Episode 2 | 2011-09-25 | 60 min |
| Season 10 | Episode 3 | Episode 3 | 2011-10-02 | 60 min |
| Season 10 | Episode 4 | Episode 4 | 2011-10-09 | 60 min |
| Season 10 | Episode 5 | Episode 5 | 2011-10-16 | 60 min |
| Season 10 | Episode 6 | Episode 6 | 2011-10-23 | 60 min |
| Production | Jane Featherstone | Executive Producer |
| Production | Gareth Neame | Executive Producer |
| Production | Simon Crawford Collins | Executive Producer |
| Production | Stephen Garrett | Executive Producer |
