The Turnstile by A.E.W. Mason

Bramling is the very house for a conspiracy. It lies in Dorsetshire, hidden away at the back of the grass-walled town of Wareham on the road to no where. A stream runs past its door down to Poole Harbor, and its windows look across grass meadows to where the sea-cliffs lift against the sky. Hither through one October day came in old-fashioned flies and private motor-cars the inhabitants of the Cave -- Cynthia amongst the last of them with a foot which hesitated to cross the threshold. There were thirty in all assembled in the drawing-room when the dinner-gong sounded, eighteen men and twelve women. Colonel Challoner, to Cynthia's satisfaction, had to give his arm to Lady Lorme, the wife of an ex-Under Secretary of the home office who had quarreled with his chief and resigned. She herself was taken in by Robert Brook. Reluctance and curiosity struggled for mastery within her as she entered the dining-room, and took her seat.

She would not look up at the walls, yet she could hardly but look up, and she sought furtively around the dinner-table whether any noticed the picture and her resemblance to it. But no one was looking at any picture at all.