Cara tracks down soldiers from the covert unit of the British army at the heart of her investigation. As these people who handled spies in the IRA and loyalist paramilitaries spill their secrets, it becomes clear that Agent 6137 and Scap are just the tip of the iceberg. Betrayal, sex, murder. Was it really all for the greater good?

Sign up to our most popular newsletter, From the Editor. Look forward to receiving free-thinking comment and the day's biggest stories, every morning. telegraph.co.uk/fromtheeditor

Get in touch: cara.mcgoogan@telegraph.co.uk and on social media @cjmcgoogan 

Hosted on Acast. See acast.com/privacy for more information.