On 26th May 1986, the body of an undercover British agent was found by the side of a muddy lane, with a rope tied around its wrists and tape over each eye. Years later, it was reported that this murder might have been carried out by another undercover British agent, known as 'Stakeknife'.

In 2016, a detective began to investigate this case, and would soon find himself running the largest murder investigation in British history.

In a compulsive blend of investigative journalism and true crime thriller, Henry Hemming exposes the parallel worlds of the IRA and British intelligence through the lives of those inextricably bound up in both. He reveals the bravery of those who were crucial in ending the Troubles in Northern Ireland, the bloodiest and longest-running conflict in recent British history, and the determination of one detective in his dogged search for justice and the truth.