perfect," he said, as he replaced the cap and closed the shutter.

He reversed the dark slide and made another exposure in the same way, and then, having removed the micrometer and replaced it by a slip of plain glass, he made two more exposures.

"There are two plates left," he remarked, as he drew out the second dark slide. "I think I will take a record of the blood-stain on them."

He accordingly made two more exposures—one of the larger blood-stain and one of the smaller smears.

"There," said he, with an air of satisfaction, as he proceeded to pack up what the inspector described as his "box of tricks." "I think we have all the data that we can squeeze out of Scotland Yard, and I am very much obliged to you, Mr. Singleton, for giving so many facilities to your natural enemy, the counsel for the defence."

"Not our natural enemies, doctor," protested Mr. Singleton. "We work for a conviction, of course, but we don't throw obstacles in the way of the defence. You know that perfectly well."

"Of course I do, my dear sir," replied Thorndyke, shaking the official by the hand. "Haven't I benefited by your help a score of times? But I am greatly obliged all the same. Good-bye."

"Good-bye, doctor. I wish you luck, though I fear you will find it 'no go' this time."

"We shall see," replied Thorndyke, and with a friendly wave of the hand to the inspector he caught up the two cases and led the way out of the building.