Bowman said, ‘One of them had something hanging out of his jacket pocket. I didn’t know what it was at the time. Or at least, I couldn’t remember where I’d seen it before. It’s a respirator strap.’

‘Why would a couple of BGs be carrying respirators?’

‘To protect them from the nerve agent,’ Bowman explained. ‘They would have needed gloves too, probably. They must have followed Lang into the toilets, put an out-of-order sign outside and then jumped him. That’s how I would have done it.’

Studley puckered his brow. ‘Let me see if I’ve got this right. You’re suspicious, because of some fucking strap you glimpsed for half a second?’

‘Why else would they be carrying masks around?’ He pointed to the corridor. ‘We’ve got a witness who says Lang told him he was mugged in the toilets. We need to get hold of the CCTV footage. That’ll show us what those BGs were up to.’

‘But we can’t be sure he was attacked here,’ said Studley. ‘How do you know he didn’t drink it in his morning tea?’

Bowman shook his head. ‘The BGs had something to do with this. I’m sure of it. We need to find them.’

Studley said, ‘I’ll ask the suits at Five and Six to look into it. But if they are involved, they’ll be long gone by now.’

‘We should notify the other guys,’ Bowman said. ‘Tell them they’re not needed at the hotel anymore. Now that we know that this guy isn’t the principal.’

‘I’ll take care of it.’

Studley’s phone hummed. He moved away to take the call, barked a few words down the line before he hung up again.

‘Officers from Counter Terrorism Command are on their way,’ he said to Bowman. ‘They’ll want a word with you, I imagine. Someone from the Cell is heading over as well.’

‘The Cell?’ Bowman frowned. ‘What’s their involvement?’

‘How would I know?’ Studley replied moodily. ‘No one ever tells us anything about them.’

Bowman looked away, his mind racing ahead of him. Every SAS man had heard of the Cell. It was a covert unit within the Wing, a small inner circle of veteran SAS men tasked with carrying out clandestine operations at home and abroad. The guys in the Cell kept a low profile: no one outside the unit knew anything about their activities, except that they worked closely with the security services and the police. In a world of shadow warfare, fought between non-state actors, the Cell was the ultimate deniable force.

And now they wanted to speak with Bowman.

What was their interest in this op? Why would they care about a hit on Freddie Lang?

And what do they want with me?