Stakeknife was a super-spy, a secret agent working for both the British and the IRA who walked a precarious tightrope in an undercover war where exposure meant death. Operation Kenova, the long-running investigation into Stakeknife and the so-called dirty war, is now coming to a close, bringing reporter Peter Taylor back to Northern Ireland. He revisits the chilling IRA interrogation tapes he initially uncovered and talks again to grieving families devasted by the loss of their loved ones to the IRA's brutal interrogators and killers