Mrs Marsh is staring at you across the red lamp, and she knows now that something at her table is not hers. The candle has burnt to its second mark.

Mark Three: The Adventure of the Marked Plates

The darkroom was a still-room once: there are still bunches of herbs hanging from the beam, so old they have no smell. Sir Arthur's photographer took four plates of Edmund at the kitchen hearth at nine o'clock this evening and developed them here, and they are drying in the rack under the red safelight.

Sir Arthur says the photographer is a man of absolute integrity, whatever was said in February about another photographer, and that two of the plates show the boy as plainly as he has ever seen a spirit shown.

Edmund says nothing for a long time. Then he says that he read about February in the papers, every word, and that before he handed over his plates he did exactly what the investigator had done. He will not say what. There is a pin in his lapel.

You hold each plate up to the safelight and look at it the way Sir Arthur says Holmes would, at everything:

A  Kit behind Edmund,
   smiling. Clock on the
   mantel: ten to six.
   One corner chipped.
B  Kit again, the same
   smile, the same tilt
   of the head. Clock:
   nine. A thumbprint.
C  Edmund alone. Clock:
   nine. In one corner,
   three specks in a
   triangle.
D  Edmund, and behind
   him a girl kneeling at
   a fire. Clock: nine.
   In one corner, three
   specks in a triangle.

The kitchen grate has been cold since 1912. Edmund had it swept when he bought the house, and has never let anybody light it.

Tap the plate that can be trusted and shows something nobody put there.