From deep within the folds of cloth he fished out a brown paper bag, holding it up proudly.

‘Here we go then. Step up, lad, and witness a miracle of human ingenuity—the smell signal!’

‘The what?’

‘Aye. Robert, you know, her—’ and here he jerked his head towards where Theo was standing, ‘—grandad came up with these. Brilliant, I tell you! Think about it. They built those damn machines to be better than us in every way. They see better’n us, hear better’n us, sense stuff you wouldn’t even imagine was goin’ on. What they can’t do, though, is smell. And so we have smell signals!’

With the flourish of a magician unveiling his greatest trick he pulled something out from the depths of the bag. It was a small object that resembled nothing so much as a liquid-filled glass ball.

‘All right, we’re all set. Don’t breathe too deep now!’

Chuckling quietly, he took a step forward and then, carefully placing the glass ball on the ground, brought his heel sharply down upon it, making sure to cover his nose with his hand first.

A moment later Albert realized why, as the worst, most horrible, vilest stench he had ever encountered shot up his nose. It was bottled evil—it was the gaseous equivalent of a fission warhead—it was excreta dipped in landfill, mixed with flatulence and lovingly immersed in the several-day-old odour of death. And it was even worse than that. It was a smell so bad it could have driven a bad smell away. So sharp was it that he could feel his nose stinging and his stomach wrench, forcing the bile up his throat. He gagged, bringing a hand up to his mouth, only just managing to control himself in time.

He turned to June who was standing on his right, holding a handkerchief against her nose and mouth. As he looked at her, his eyes streaming, she handed him one as well.

‘Cover your nose and breathe through your mouth,’ she said, her voice muffled through the cloth.

He complied, blinking at her gratefully. Looking around, he saw Theo, who was standing there, not even bothering to cover her nose. She seemed completely unaffected by the pungency of the air around. Spotting him staring at her, she gave him a thumbs-up signal and grinned.

‘Wuss,’ she mouthed.

Even through the handkerchief, the smell was unbearable.

‘All right, time to move in,’ said Ollie. ‘In groups of two, just to be safe. You and me first, friend.’