White Suit didn’t move, other than to throw a nod at the small video camera mounted on the dusty stone shelf nearby, between a set of false teeth and an old military medal, a tiny point of green light indicated that it was active. ‘He said you have to do it on your own. And he’s filming us. Just to make sure you do as you’re told.’

Yellow Suit turned back to the drum. ‘If I get burned, it’s your fault.’

‘Nope. It’s your fault.’

Being more careful now than at any stage so far, checking first the seals between gauntlets and sleeves, Yellow Suit slid around to the back of the drum on the left, and gingerly reached out to the facing edges of its rim, taking a firm grip, and then slowly rotating it and shuffling it forward. It was hugely heavy, and its dark contents, slopping from side to side, constantly threatened to overbalance it. Thankfully, the distance to the sewer shaft was no more than a yard. And Yellow Suit didn’t even have to go that far, before halting, with both hands now tight on the closest section of rim. As cautiously as possible, body braced backward to ensure that it didn’t get away, the drum was gradually allowed to tilt forward.

With heavy glops, gurgles and thick, steamy emissions, the sludgy brown contents began disgorging, dripping slowly but steadily down the hole. When the drum had lightened sufficiently, Yellow Suit brought it back upright and drew it backward a foot, then tilted it forward again, this time to the horizontal. A vomit-like stream spilled downward. It contained various shapeless solids, and whenever globules of it spattered the rock at the rim of the pipe or down the inside, it hissed violently, issuing oily, greasy smoke – but the vast bulk of it vanished into the subterranean stream, all that remained of the late Harry Hopkins fastidiously flushed away.

‘You know, this stuff doesn’t get rid of everything,’ Yellow Suit said, when the job was done, shoving the empty drum back into place. ‘If they ever decide they want to use this building—’

‘We block that sewer with cement before we scarper,’ White Suit cut in. ‘As planned.’

Yellow Suit brought the first bucket of water over and sloshed it down the pipe. Then grabbed the second and doused the one or two smouldering spots on the flagstones surrounding the aperture. ‘You don’t think they’d find that a bit unusual?’