1983: as the country goes to the polls, two "Urban Explorers", together with a freelance journalist, break into the long-defunct Cadogan Tunnels, once a secret wartime facility... and later, so rumour has it, the site of an experimental laboratory with a nasty sideline in vivisection. What they find, in its twisting underground corridors, is something the most cynical conspiracy theorist could never have imagined: a highly-evolved society of questing, intelligent creatures, living right under humanity’s nose for decades.