What concerned him was the lack of thought given to Herm, whom he and Gareth had recruited many years ago. Herm was then a medical student in London, an Afghan refugee whose residency status was unclear even to the Home Office. He had been interviewed by MI5 about a terrorist he was thought to know and, as he had run out of money and was about to give up his training and return to Afghanistan, he had been passed to MI6 as a possible useful contact. Charles, then London-based, had been asked to assess him. He found a stocky, serious-minded, seemingly fearless young man who hated al-Qaeda and the Taliban for the damage they had wrought upon his country and was prepared to work against them. Charles persuaded him he should finish his training, discreetly funded by MI6 on the understanding that he would remain in contact when he returned to Afghanistan. Before he left Charles handed him over to Gareth, who was about to join the Kabul station. Gareth handled him well and during his Kabul tour turned Herm into a useful source on extremists he came across through his wide-ranging medical practice.

Charles had then lost sight of the case until recently learning that Herm was still on the books as a doctor in IS-occupied Syria, co-operating with IS for the sake of his patients but secretly reporting via a young case officer who crossed the border from Iraq for clandestine meetings under Special Forces protection. Tresco/1 had come to Herm as a patient with a slight shrapnel wound. Finding that his doctor knew London, he had sought his advice on key points and bomb targets. Herm had obliged and reported back. After witnessing Tresco/1 executing two teenage Syrian boys, supposed spies, and a French journalist, he had offered to plant a homing device so that Tresco/1 could be killed. Tresco/1 changed his mobile phone frequently, but it was always the same kind and from the same supplier. Herm was provided with an identical doctored handset, which he was to substitute for Tesco/1’s latest when occasion arose.