"It's not often used," said Master Sean. "It is a psychic phenomenon that sometimes occurs at the moment of death—especially a violent death. The violent emotional stress causes a sort of backfiring of the mind, if you see what I mean. As a result, the image in the mind of the dying person is returned to the retina. By using the proper sorcery, this image can be developed and the last thing the dead man saw can be brought out.
"But it's a difficult process even under the best of circumstances, and usually the conditions aren't right. In the first place, it doesn't always occur. It never occurs, for instance, when the person is expecting the attack. A man who is killed in a duel, or who is shot after facing the gun for several seconds, has time to adjust to the situation. Also, death must occur almost instantly. If he lingers, even for a few minutes, the effect is lost. And, naturally if the person's eyes are closed at the instant of death, nothing shows up."
"Count D'Evreux's eyes were open," Dr. Pateley said. "They were still open when we found him. How long after death does the image remain?"
"Until the cells of the retina die and lose their identity. Rarely more than twenty-four hours, usually much less."
"It hasn't been twenty-four hours yet," said Lord Darcy, "and there is a chance that the Count was taken completely by surprise."
"I must admit, my lord," Master Sean said thoughtfully, "that the conditions seem favorable. I shall attempt it. But don't put any hopes on it, my lord."
"I shan't. Just do your best, Master Sean. If there is a sorcerer in practice who can do the job, it is you."
"Thank you, my lord. I'll get busy on it right away," said the sorcerer with a subdued glow of pride.
Two hours later, Lord Darcy was striding down the corridor of the Great Hall, Master Sean following up as best he could, his caorthainn-wood staff in one hand and his big carpet bag in the other. He had asked Father Bright and the Countess D'Evreux to meet him in one of the smaller guest rooms. But the Countess came to meet him.