Then, as the policeman staggered with the swing of the blow he had aimed, the invisible man countered with the axe, the helmet crumpled like paper, and the blow sent the man spinning to the floor at the head of the kitchen stairs. But the second policeman, aiming behind the axe with his poker, hit something soft that snapped. There was a sharp exclamation of pain and then the axe fell to the ground. The policeman wiped again at vacancy and hit nothing; he put his foot on the axe, and struck again. Then he stood, poker clubbed, listening intent for the slightest movement.

He heard the dining room window open, and a quick rush of feet within. His companion rolled over and sat up, with the blood running down between his eye and ear. “Where is he?” asked the man on the floor.

“Don’t know. I’ve hit him. He’s standing somewhere in the hall. Unless he’s slipped past you. Doctor Kemp⁠—sir.”

Pause.

“Doctor Kemp,” cried the policeman again.