channel from a different tributary, this one bringing in floating islands of animal fat from a riveted lead pipe. The stench of rotted meat and sewage caused Bimsley to throw up his lunch over a blocked drain.
‘The construction of these tunnels is remarkable,’ Bryant enthused. ‘Look at this metalwork, you don’t find craftsmanship like that any more. And the decoration—why would anyone bother to put a neoclassical bay-leaf-garland motif around an arch that no one will ever see? That’s Victorian pride for you.’
‘Jesus, there’s bloody great big rats down here.’ Bimsley hopped on to one foot and banged his skull on the ceiling, shattering calcified stalactites as a bedraggled squeaking creature with matted fur shot past him.
‘Don’t be such a baby,’ said Bryant, turning the map around. ‘John, we need to concentrate all our lights, please.’
They forked left at a pair of yellow-brick arches coated in slender black tree roots.
‘We must be under Prince of Wales Road, heading toward the Regent’s Canal by now. Look, there are plaques.’ May pointed to the conduit’s brass nameplate bolted into the wall, a subterranean echo of the street names on the roads above.
Bryant’s torch-beam fell on what appeared to be a bundle of rags. ‘Tate’s jacket. He wants us to follow him.’
‘For the life of me I don’t understand why,’ said May.
‘Oh, he’s been waiting for this since the rains began.’
‘Does Mr Bryant know something we don’t?’ asked Bimsley, confused.
‘Mr Bryant always knows something we don’t,’ May admitted. ‘We’re going to need inoculations after this.’
‘Perhaps, but we’ll have learned something new.’ Bryant shone the torch over the tunnel arch. A wider channel ran crossways, like the junction of an arterial road. Shallow, cleaner water was flowing fast through it. ‘I don’t weigh very much. Think we can get across that?’
‘Hang on to me. Bimsley, you’re the heaviest, lad—you lead.’
The trio clutched each other’s hands and waded out, but Bryant was nearly pulled off his feet. May and the detective constable yanked him to the other side like parents controlling a recalcitrant child.
‘Look at this.’ May pointed to the wall beside them. ‘One of your fail-safe conduits.’ He slapped his hand on the riveted steel panel, layered with grease and grooved at its base to shift around a matching steel arc, like the flood gate in an underground station. Behind a grille at the top, water was rushing away into darkness. ‘If the water rises too high, it’ll come over and re-flood this tunnel, creating a run-off.’
‘Some of these tunnels look dry,’ Bimsley pointed out.
‘I don’t think we’ve reached the part of the system designed for peak flooding yet,’ said Bryant. ‘We’ll know it when we see it.’
From here the floor sloped downwards, and they found themselves going deeper. ‘According to this, there’s an emergency escape drain above us, but I don’t see it.’ May waved his torch about.
‘There,’ said Bimsley, illuminating a narrow round shaft far above them. ‘It looks like the ladder has rusted away and fallen in.’
‘That’s reassuring.’
Following the map to the St Pancras Basin, they turned into a narrower ramped tunnel with slender iron platforms on either side. ‘This is part of the system newly exposed by the flood switches,’ said Bryant. ‘Look at the walls.’ They showed clear signs of long-term immersion. Strangely, the stone floor beneath their feet was less slippery, and the air smelled healthier. ‘Nothing’s had time to stagnate here. It’s probably been kept full just coping with the natural run-off of freshwater from Hampstead Heath and the other high areas above the city. It isn’t wide enough to cope with severe flooding, but it’s fine for everyday use. Wonderful workmanship; not a stone out of place. Beautiful bevelling.’
Bimsley’s radio crackled, making him jump. ‘The rain’s easing up,’ warned Longbright. ‘You’d better start heading for the nearest exit.’
‘We must be nearly there.’ Bryant waded on ahead. ‘The light is less dense.’
He was right. A faint sickly glow changed the colour of the walls before them, but as they approached, they found themselves entering a network of claustrophobic culverts, each one barred at the end.
‘We’ll have to turn around,’ May warned. ‘This one’s a dead end too.’
‘Interesting,’ said Bryant, seemingly unconcerned that they might be swept away at any minute. ‘I’m assuming that Tate is down here looking for something that has been unexposed for some thirty years, and I would have thought that this was the most likely place for him to be. The tunnels fill to their highest level, then empty, washing everything out this