They sent him back to the detention-room where, with a constable seated opposite to him, he was to spend the night. Foyle rested one arm on the mantelpiece and kicked the fire viciously into a blaze.
"Ours is an ungrateful business, Sir Hilary," he grumbled, "but I've never come across a man who put so many difficulties in the way of being saved from the gallows as Mr. Robert Grell."
Thornton took a long breath that was almost a sigh. "Poor chap," he said reflectively. "Poor chap!" And then, after an interval, "Poor girl! Couldn't you have dropped a hint, Foyle?"
The introduction of sentiment into business was a folly that Heldon Foyle seldom permitted himself. With a shrug he pulled himself together. He shook his head. "We've got to be more certain yet. I daren't tell him too much—for my idea may prove to be wrong. You must remember that it was undoubtedly Eileen Meredith's finger-prints on the dagger. At present it is only surmise of mine how they got there. Finding the prints on her blotting-pad, which I showed you, corresponded with those on the dagger you gave me, was one of the biggest surprises of my life. But we may clear it up now."
"H'm," said Thornton. "Well, we shall have to look sharp."
A thought struck Foyle. He stood rigid as a statue for a moment, and then slapped his knee with sudden energy, "By God! I believe I've got it!" he exclaimed, and jumped for the telephone.
"Put me through to the Yard.... Hello! I want Mr. Grant.... That you, Grant?... About the Grosvenor Gardens case. Tell me. Might the finger-prints on the dagger have been caused by some one withdrawing it and replacing it after the murder had been committed? Would the second handling have obliterated first prints?... Blurred them. I see. But if the person who first handled the dagger wore gloves? Thanks. That's what I wanted to know."
He replaced the receiver and turned triumphantly on Thornton. "That bears out my idea, Sir Hilary. Will you excuse me while I see if Bolt's on the premises?"
Without waiting for a reply, he darted from the room. The Assistant Commissioner's brow puckered and he thoughtfully replaced the upset furniture. By the time he had finished Foyle had returned.