The second policeman began struggling to his feet. He stood up. Suddenly the faint pad of bare feet on the kitchen stairs could be heard. “Yap!” cried the first policeman, and incontinently flung his poker. It smashed a little gas bracket.

He made as if he would pursue the invisible man downstairs. Then he thought better of it and stepped into the dining room.

“Doctor Kemp⁠—” he began, and stopped short.

“Doctor Kemp’s a hero,” he said, as his companion looked over his shoulder.

The dining room window was wide open, and neither housemaid nor Kemp was to be seen.

The second policeman’s opinion of Kemp was terse and vivid.