The Reading Room was a strangely deserted place when they entered it. The caretaker had switched on the lights, but the tall, domed room, its shadows fading off into the mysterious darknesses of the roof, was curiously eerie and weird. Cunningham, hard-boiled materialist though he was, found himself shuddering and glancing behind him as if he feared that some unseen assassin was on his track.

But, in spite of Shelley’s insistent “hunch,” they found no trace of Dr. Crocker. There was not a soul in the room except themselves. They peered behind desks and under tables. Shelley even insisted on going up to the metal galleries which run around the room, but the place was deserted and still as the grave.

Shelley’s temper, which had been bad enough before, was now in the vilest mood that Cunningham had ever seen it. The inspector was hungry, thirsty, tired, and sleepy. He had worked very hard for several hours, and he felt that he had nothing to show for it.

“Back to the Yard,” he said shortly, and they made their way to the door, the caretaker locking the doors behind them, and escorting them down to the big iron gates which led to Great Russell Street.

As they approached the gates Shelley looked around him with sudden interest.

“What’s that?” he asked.

“What’s what?” asked Cunningham in his turn.

“That…over there,” said Shelley, pointing.

Cunningham looked in the direction indicated, but could see nothing at all.

“Has it been raining at all today?” asked Shelley.

“Why, no,” said Cunningham.

“Well, there’s a pool of something on the concrete path over there,” said Shelley. “I caught a flash as the light of the street lamp was reflected in it.”

“Expect that they’ve been washing the path,” Cunningham suggested, but Shelley laughed the idea to scorn.

“Do you really think so?” he asked. “Well, let’s have a look at it. Have you got a torch with you?” Cunningham nodded. “Well, get it out, and then we can see.”

They strode towards the spot that Shelley had indicated, and Cunningham produced his electric torch, shining it at his chief’s directions. There was certainly a pool of liquid there. But the liquid was not water.

“What the devil?” Cunningham muttered.

“Not the devil,” Shelley corrected him, with an eerie chuckle. “The murderer.”

“What do you mean, sir?” Cunningham asked.

Shelley stooped and touched the little pool of liquid. It was unpleasantly sticky.

“Blood, Cunningham,” he said. “There’s been something very queer going on whilst we were inside that building.”

Cunningham was flashing the light around him, trying to pierce the gloom and to see whether there was any sensible explanation of this strange affair.

“Look!” he suddenly exclaimed, and Shelley looked at the torch-beam, cutting the darkness like a knife.