They began with the obvious omissions.

The next morning, while Dyson was engaged with a class and the Dean was safely confined to a meeting about repairs, Lomas and Makepeace requested the presence of Mr Corbett, the Head Porter of the College, and the Reverend Mr Allwood, the Chaplain.

They met in a small, draughty parlour off the College cloister, where a dying fern clung to life in a cracked pot.

Corbett arrived first. He was a thick–set man in his fifties with side whiskers and a permanently suspicious expression, as if life had offended him early and often.

“You’ll be wanting to know who goes in and out,” he said, before they had asked a question. “That’s what porters know. That’s what we’re for.”

“Yes,” Lomas said....

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