Stuart is a freelance surveillance expert who teaches "covert information gathering" to new intelligence recruits.

As part of his work he "bugs" friends and family, including his wife, Penny. When he discovers that she's having an affair with a man called Neil, his work colleague, Ren, offers her own skills in "enhanced interview techniques" to help, but Stuart declines.

He realises that the secret affair could make an engaging teaching aid. Initially, his students are slightly unsettled but very intrigued. The affair becomes the main focus of the curriculum, and the group study how to bug all manner of difficult situations, such as an impromptu hotel room, a car in a field, a busy nightclub and a hot-air balloon. But Penny feels terrible about the affair and, when Stuart discovers emotions deeply buried, things soon spiral out of control.