One of the best-known photographs of Edward Thomas (1878–1917) was taken a century ago this year. It is a studio portrait: Thomas is seated but leaning forwards, his chin resting on the knuckles of his folded hands. A white light falls from right of frame, lending a lustre to his hair, a glint to his eyes and a glitter to the signet ring on his left little finger. His features are fine, fawnish and in focus; his tweed jacket and shoulders disappear backwards into a blur. Unsettlingly, Thomas’s gaze is not directly outwards, but angled steadily away at something behind and to the right of the camera. When I first saw the photograph, I wanted to glance over my shoulder and glimpse what it was that had so drawn Thomas’s attention.