The two constables were instantly on the alert. They examined the lock of the front door, conversing in low whispers, then, after a brief consultation, one of the pair left hurriedly, in order to place a guard upon the front of the premises, overlooking the garden, which divided the crescent from the park. Presently he returned, accompanied by a brown-bearded sergeant, who recognised Langton as having been witness in a motor-car accident in Cumberland Terrace a couple of months before. The sergeant pressed the button of the electric bell for a long time, and though we waited anxiously there was, of course, no response. "I'm certain somebody is within," declared Langton excitedly; "I saw the light quite distinctly." "Very well, sir, if you're certain," replied the sergeant gruffly, "we'll have to force an entry. But remember, if you're mistaken, it will be a trifle awkward. The owner might come upon you for damage." "I'll stand the racket of all that," declared the young man readily. "There are thieves in here, I'm certain." "It may be only a maid who has a visitor, and who believes her master, or young mistress, has returned," I suggested, full of apprehension at the alarming discovery which must be made as soon as the police entered and searched the place. "Then all the worse for her, sir," answered one of the constables grimly. And again they banged at the door and continued ringing. All, however, was silence and darkness. What would they have thought had they known that I had allowed the mysterious Kirk, who had been lurking there, to escape? Had I acted foolishly in doing so? I was forced to the conclusion that I had. While sergeant and constables were in counsel as to what course should be adopted, an inspector, who had been warned by the constable on guard at the front, arrived, and was told Langton's story. "This is Professor Greer's," he remarked; "I think we'd better force an entry, sergeant. That basement window down there looks easy of access," and he pointed to a window of the back-kitchen. "Yes," replied the bearded man addressed, as a constable shone his lantern down upon it, "we could break the glass and turn back the catch. There are no bars there." This course was quickly adopted. The inspector, taking one of the men's truncheons, tapped the glass lightly until he had cracked it, and then pulled the pieces forward till he could insert his hand and release the catch. The window thus opened, the two constables, truncheons in hand and lights turned on, crept into the kitchen and disappeared, while we stood waiting anxiously without, our ears strained in listening. A few moments later, one of the men threw open the front door, and together we entered the dark and silent house of mystery. I stood back, passing into the wide hall last of all. There was now no hiding the grim, astounding truth from police and public. I held my breath, awaiting the sensation that must be caused by the discovery.