She went across to the Holbein portrait, touched a spring concealed somewhere at the side of it, and immediately, with a creaking noise, a section of the panelling swung inward, revealing a dark opening.

“ Entrez, Messieurs et Mesdames ,” said Bundle dramatically. “Walk up, walk up, dearies. Best show of the season, and only a tanner.”

Both Lemoine and Battle were provided with torches. They entered the dark aperture first, the others close on their heels.

“Air’s nice and fresh,” remarked Battle. “Must be ventilated somehow.”

He walked on ahead. The floor was of rough uneven stone, but the walls were bricked. As Bundle had said, the passage extended for a bare hundred yards. Then it came to an abrupt end with a fallen heap of masonry. Battle satisfied himself that there was no way of egress beyond, and then spoke over his shoulder.