“A good idea,” he assented.  “But—­there are windows, of course, and there is nothing to prevent whoever is in there from getting out that way.”

“Then lock the door at the top of the basement stairs,” I suggested, “and patrol the house from the outside.”

We agreed to this, and I had a feeling that the mystery of Sunnyside was about to be solved.  I ran down the steps and along the drive.  Just at the corner I ran full tilt into somebody who seemed to be as much alarmed as I was.  It was not until I had recoiled a step or two that I recognized Gertrude, and she me.

“Good gracious, Aunt Ray,” she exclaimed, “what is the matter?”

“There’s somebody locked in the laundry,” I panted.  “That is—­ unless—­you didn’t see any one crossing the lawn or skulking around the house, did you?”

“I think we have mystery on the brain,” Gertrude said wearily.  “No, I haven’t seen any one, except old Thomas, who looked for all the world as if he had been ransacking the pantry.  What have you locked in the laundry?”

“I can’t wait to explain,” I replied.  “I must get Warner from the lodge.  If you came out for air, you’d better put on your overshoes.”  And then I noticed that Gertrude was limping—­not much, but sufficiently to make her progress very slow, and seemingly painful.

“You have hurt yourself,” I said sharply.

“I fell over the carriage block,” she explained.  “I thought perhaps I might see Halsey coming home.  He—­he ought to be here.”

I hurried on down the drive.  The lodge was some distance from the house, in a grove of trees where the drive met the county road.  There were two white stone pillars to mark the entrance, but the iron gates, once closed and tended by the lodge-keeper, now stood permanently open.  The day of the motor-car had come; no one had time for closed gates and lodge-keepers.  The lodge at Sunnyside was merely a sort of supplementary servants’ quarters:  it was as convenient in its appointments as the big house and infinitely more cozy.

As I went down the drive, my thoughts were busy.  Who would it be that Mr. Jamieson had trapped in the cellar?  Would we find a body or some one badly injured?  Scarcely either.  Whoever had fallen had been able to lock the laundry door on the inside.  If the fugitive had come from outside the house, how did he get in?  If it was some member of the household, who could it have been?  And then—­a feeling of horror almost overwhelmed me.  Gertrude!  Gertrude and her injured ankle!  Gertrude found limping slowly up the drive when I had thought she was in bed!

I tried to put the thought away, but it would not go.  If Gertrude had been on the circular staircase that night, why had she fled from Mr. Jamieson?  The idea, puzzling as it was, seemed borne out by this circumstance.  Whoever had taken refuge at the head of the stairs could scarcely have been familiar with the house, or with the location of the chute.  The mystery seemed to deepen constantly.  What possible connection could there be between Halsey and Gertrude, and the murder of Arnold Armstrong?  And yet, every way I turned I seemed to find something that pointed to such a connection.