Thorndyke laughed grimly. “It was a perfectly asinine mistake, Jervis. You started up Kennington Park Road on a leisurely, jog-trotting omnibus, and neither you nor I remembered what there is underneath Kennington Park Road.”

“Underneath!” I exclaimed, completely puzzled for the moment. Then, suddenly realizing what he meant, “Of course!” I exclaimed. “Idiot that I am! You mean the electric railway?”

“Yes. That explains everything. Mrs. Schallibaum must have watched us from some shop and quietly followed us up the lane. There were a good many women about and several were walking in our direction. There was nothing to distinguish her from the others unless you had recognized her, which you would hardly have been able to do if she had worn a veil and kept at a fair distance. At least I think not.”