He batted away the daydream and focused on his document, but nothing came to mind except a bunch of lame excuses, none of which would wash with Huxtable.

Sod it.

He looked up from his terminal and across at the screens. One news channel showed the centre of Tunis teeming with military personnel, another a beach full of parasols and sun loungers but devoid of tourists. A third focused on the glossy black door at Downing Street. A caption said the prime minister would shortly be making a statement.

‘It was you, Taher,’ Holm whispered to himself. ‘I know it was.’

As soon as he’d spoken he looked up to check nobody had overheard. The mere mention of Taher’s name would have Huxtable frothing at the mouth. For her, Taher was a sign of Holm’s failings. The single-mindedness that had served him well when he’d been in Special Branch was frowned upon here. Phrases like the bigger picture, a connected world, and – Holm’s favourite meaningless platitude – one bullet doesn’t end a war, went down well. Holm’s old-fashioned ideas did not. You didn’t wear out shoe leather these days and you didn’t cultivate informants in smoky back-room bars. You didn’t chase after a man the security services were beginning to think was a myth deliberately propagated by the terrorists to confound their enemies.

Holm had to admit there wasn’t much to go on. The first time the intelligence services had come across Taher had been in text messages found on a number of mobile phones that had been discovered in the UK, France and Belgium. Local ISIS operatives mentioned a free agent who was revered as some kind of emerging jihadi superhero. For a number of years he’d been rumoured to have been involved in almost every atrocity that had taken place in Europe. If he wasn’t actually there, then he was the one doing the planning and supplying the means and the money. However, recently the leads had dried up, leaving behind nothing but speculation. Even Holm’s most trusted informant had changed his tune.

‘You want to believe, then you believe,’ he’d said. ‘But I’ve come to the conclusion Taher is no more than a straw man you’ve created to justify your failures.’

It was true that almost everything about Taher was unsubstantiated: his age, background, country of origin. Was he a refugee or home grown? British, French, German, Belgian? Did he wear his beliefs on his sleeve or was he in some form of deep cover? Was he in a relationship? Did he have a job? Where did he get his money from? Was he, in fact, a composite of more than one individual?