Parker interposed deferentially. “If you’ll excuse me, sir. If you were to lock the door into the main hall, nobody could gain access to this part of the house. That staircase leads only to Mr. Ackroyd’s bedroom and bathroom. There is no communication with the other part of the house. There once was a door through, but Mr. Ackroyd had it blocked up. He liked to feel that his suite was entirely private.”

To make things clear and explain the position, I have appended a rough sketch of the right-hand wing of the house. The small staircase leads, as Parker explained, to a big bedroom (made by two being knocked into one) and an adjoining bathroom and lavatory.

The inspector took in the position at a glance. We went through into the large hall and he locked the door behind him, slipping the key into his pocket. Then he gave the constable some low-voiced instructions, and the latter prepared to depart.