Slim Parsons’ last deep cover job for MI5 ended with a life-and-death struggle on a private jet that caused her to go on the run from both the deadly target and her angry bosses in the Security Service. They say that she’s bordering on delinquent and unsuitable for the role of an MI5 operative. Yet she is recalled and asked to infiltrate a news website that’s causing alarm. It is staffed by a group descended from wartime codebreakers operating from an unassuming office block near Bletchley Park. Operation Linesman looks like a come down, the curtain on a brilliant career in the shadows. However, she accepts the assignment on condition that the Security Service searches for her missing brother. Linesman turns out to be anything but simple. Her personal loss, her previous deep cover role, and a threat to MI5 itself from her original target come together in a three-way collision.