“How long should you say she’d been dead, sir?” he asked affably.

“About ten hours,” replied Thorndyke.

The inspector and the detective simultaneously looked at their watches.  “That fixes it at two o’clock this morning,” said the former.  “What’s that, sir?”

The surgeon was pointing to the wisp of hair in the dead girl’s hand.

“My word!” exclaimed the inspector.  “A woman, eh?  She must be a tough customer.  This looks like a soft job for you, sergeant.”

“Yes,” said the detective.  “That accounts for that box with the hassock on it at the head of the bed.  She had to stand on them to reach over.  But she couldn’t have been very tall.”

“She must have been mighty strong, though,” said the inspector; “why, she has nearly cut the poor wench’s head off.”  He moved round to the head of the bed, and, stooping over, peered down at the gaping wound.  Suddenly he began to draw his hand over the pillow, and then rub his fingers together.  “Why,” he exclaimed, “there’s sand on the pillow—­silver sand!  Now, how can that have come there?”

The surgeon and the detective both came round to verify this discovery, and an earnest consultation took place as to its meaning.

“Did you notice it, sir?” the inspector asked Thorndyke.

“Yes,” replied the latter; “it’s an unaccountable thing, isn’t it?”

“I don’t know that it is, either,” said the detective, he ran over to the washstand, and then uttered a grunt of satisfaction.  “It’s quite a simple matter, after all, you see,” he said, glancing complacently at my colleague.  “There’s a ball of sand-soap on the washstand, and the basin is full of blood-stained water.  You see, she must have washed the blood off her hands, and off the knife, too—­a pretty cool customer she must be—­and she used the sand-soap.  Then, while she was drying her hands, she must have stood over the head of the bed, and let the sand fall on to the pillow.  I think that’s clear enough.”

“Admirably clear,” said Thorndyke; “and what do you suppose was the sequence of events?”

The gratified detective glanced round the room.  “I take it,” said he, “that the deceased read herself to sleep.  There is a book on the table by the bed, and a candlestick with nothing in it but a bit of burnt wick at the bottom of the socket.  I imagine that the woman came in quietly, lit the gas, put the box and the hassock at the bedhead, stood on them, and cut her victim’s throat.  Deceased must have waked up and clutched the murderess’s hair—­though there doesn’t seem to have been much of a struggle; but no doubt she died almost at once.  Then the murderess washed her hands, cleaned the knife, tidied up the bed a bit, and went away.  That’s about how things happened, I think, but how she got in without anyone hearing, and how she got out, and where she went to, are the things that we’ve got to find out.”

“Perhaps,” said the surgeon, drawing the bedclothes over the corpse, “we had better have the landlady in and make a few inquiries.”  He glanced significantly at Thorndyke, and the inspector coughed behind his hand.  My colleague, however, chose to be obtuse to these hints:  opening the door, he turned the key backwards and forwards several times, drew it out, examined it narrowly, and replaced it.