It was something after two when the door-bell rang. It rang quickly, twice. I got up drowsily, for the maids and Mrs. Klopton always lock themselves beyond reach of the bell at night, and put on a dressing-gown. The bell rang again on my way down-stairs. I lit the hall light and opened the door. I was wide-awake now, and I saw that it was Johnson. His bald head shone in the light—his crooked mouth was twisted in a smile.

“Good Heavens, man,” I said irritably. “Don’t you ever go home and go to bed?”

He closed the vestibule door behind him and cavalierly turned out the light. Our dialogue was sharp, staccato.

“Have you a key to the empty house next door?” he demanded. “Somebody’s in there, and the latch is caught.”

“The houses are alike. The key to this door may fit. Did you see them go in?”

“No. There’s a light moving up from room to room. I saw something like it last night, and I have been watching. The patrolman reported queer doings there a week or so ago.”

“A light!” I exclaimed. “Do you mean that you—”

“Very likely,” he said grimly. “Have you a revolver?”

“All kinds in the gun rack,” I replied, and going into the den, I came back with a Smith and Wesson. “I’m not much use,” I explained, “with this arm, but I’ll do what I can. There may be somebody there. The servants here have been uneasy.”

Johnson planned the campaign. He suggested on account of my familiarity with the roof, that I go there and cut off escape in that direction. “I have Robison out there now—the patrolman on the beat,” he said. “He’ll watch below and you above, while I search the house. Be as quiet as possible.”