‘Spot on. I’ve thought of that. Those small titanium pulleys the Mountain Troop use for hoisting heavy machine guns and mortars up steep hillsides. The thing is, how robust are the devices? Can they stand knocks, or have they got to be feather-bedded?’

‘Oh no, they’re pretty robust. You could probably drop one down the shaft and it wouldn’t come to any harm.’ Toad frowned and then added, ‘Cancel that. Better not drop it.’

‘But it couldn’t go off, even if we did?’

‘Not a chance. Until the two components are united they’re inert. We’ll have to take them in separately and couple them at the last minute.’

He studied the plan for a minute, then asked, ‘What depth is the tunnel running at as it comes to the Kremlin wall?’

‘We don’t know. But it’s a hell of a wall. Must be thirty or forty feet high, so the foundations have to go down some way.’

‘We’ll need to get the SCR within ten feet of the surface.’

‘The SCR?’

‘The Satellite Communications Responder. That’s the unit which the satellite sends messages to and interrogates.’

‘How big is it?’

‘Oh – those small black boxes downstairs. Didn’t you see them? Like this.’ He held up his hands a foot apart.

‘Can they be some way away from the device?’

‘Sure. The connecting co-ax cables can be any length.’

‘Maybe there’ll be an old ventilation shaft. Or maybe we’ll have to bore into the tunnel roof.’

‘An auger, then.’

‘Good thinking. What else?’

Slimy though he was, Toad had his head screwed on, and in the morning he gave the whole team a good briefing. This time he started with the SCR, and described how it needed to be positioned with its antenna coming up to within three or preferably two feet of the surface. The controlling satellite, he told us, would send it signals to check that the system was working. There was no chance of an accidental explosion, because detonation could only be achieved by a complex sequence of questions and answers, and confirmed by coded messages from the Pentagon.

‘The SCR contains its own nuclear power source, which gives it an indefinite life,’ Toad said. ‘One snag is that the generator contains radioactive fuel and could become a health hazard if it gets crushed or broken. That’s why it’s so heavy: it’s encased in a lead jacket.’

‘What happens if the Russian security forces do an electronic sweep along the front of the Kremlin, up above?’ asked Rick. ‘Won’t they detect it?’

‘Almost impossible,’ Toad replied smoothly. ‘For ninety-nine per cent of the time the SCR’s passive. It’s just listening. Its response periods will be pre-set to times like three in the morning, when people are least likely to be about.’