The characters featured include Harry Pearce, Adam Carter, Ruth Evershed, Zafar Younis, Malcolm Wynn Jones, Ros Myers and Jo Portman from the current cast and the enduringly popular Tom Quinn, Zoe Reynolds and Danny Hunter from the original line-up.
The files contain all the information that the fans could wish for, ranging from how the characters were recruited into MI5 to operational de-briefings and psychological treatment they have received and training they have endured.
Each character is brought to life in a way that the programme itself is unable to do as the book explores, in minute detail, the events that have shaped their lives and the effect their professional lives have had on them personally.