Mr Chalmers had taken rooms, of course, at the best inn in Yorbridge.

The King’s Arms occupied a corner of the Market Square, its sign creaking faintly in the wind, its windows polished to a shine that suggested an ongoing war with smoke and grime. Inside, the air smelled of beer, boiled beef and coal; the carpet in the private parlour was thick enough to muffle indiscreet footsteps.

The landlord, deferential and bursting with secrecy, led Lomas and Makepeace along a corridor lined with hunting prints.

“He’s in number four, sir,” he whispered. “Gentleman from London. Very particular. Didn’t say which Department, but you know how it is—” He tapped his nose.

“I do,” Lomas said. “We shall try not to disturb his mysteries.”...

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