‘It was, of course, a stupid, cruel and totally irresponsible prank. A moment’s thought on their part should have led them to discard it as soon as it was suggested. But they didn’t. At the appointed time, Tarrant “heard” his noises and led Miss Spencer-Brown up to the attic room.’

Paul, his stomach taut, wondered if it had been the seven-sided room or one of the others. He pictured the young man and the woman creeping up the narrow steep stair that summer night over sixty years ago, the young man hugging to himself his gleeful anticipation of his companion’s come-uppance. And the woman. Was she scared?

‘They heard nothing as they reached the top of the stairs. Tarrant said afterwards he thought Gray must have mistaken the time or forgotten he was supposed to produce some encouraging noises. So he assured the woman he could still hear raps, hoping that her imagination would feed on that.

‘When they pushed open the door of the room it was in pitch darkness. Tarrant felt tense, anticipating Gray’s sudden white-clad figure leaping towards them. But nothing happened. The student, irritated, shone his lamp inside the room, hoping that the illumination, dim as it was, would not be bright enough to show up the fact that it was his friend wearing a white sheet.’

Meredith frowned.

‘It was then that they smelled the stench pervading the room, saw something huddled under the octagonal table in the centre of the room. Holding the lamp up higher, they approached, crouched to examine the shape under the table. It was Bernard Gray, in pyjamas, the white sheet crumpled up beside him. He lay on his side, bloodless, chalky face towards them, back bent, his body drawn in to the foetus position, his eyes wide and staring and empty. He was alive but quite beyond anyone’s reach.

‘When they tried to move him they found he had evacuated both bowels and bladder. He was never able to give any account of what had happened to him. Except that he did whisper, just once: “Mummy, it was so dark . . . so dark.”

‘He remained in that catatonic state for the next twenty-three years, his mind – if it was still there at all – utterly inaccessible to every effort made to reach him. He died in a hospital for the insane in nineteen-thirty-seven.’

Carol shivered.

‘That’s horrible. Did they never find out what happened?’

‘He couldn’t tell them. But since he had been, before the practical joke that backfired, a tough, unimaginative rugby-playing healthy young man, it seems highly unlikely that he had been referring to the ordinary darkness of the room in his one utterance. No. Whatever it was, it was something that unhinged his mind completely.’

Pollard said: ‘What was the outcome of the tragedy?’