"Thank God!" she gasped, as though a great weight had been lifted from her mind. "Thank God that I have found you. The tide is rising, and in half an hour you would have been beyond human aid." "The tide!" I repeated. "What do you mean?" "At high tide the river floods this place to the roof, therefore nothing could have saved you." "What place is this?" The voice was silent, as though hesitating to reveal to me the truth. "A place wherein, alas! more than one person has found his grave," she explained at last. "But I don't understand," I said eagerly. "All is so puzzling. I believed that I was inside a police-station, whereas I had actually walked into this mysterious and cleverly-prepared trap. Who are these people who are my enemies?--tell me." "Unfortunately, I cannot." "But you, yourself, are not one of them," I declared. "I may be," answered the voice in a strange, vague tone. "Why?" "Ah! no, that is not a fair question to ask." "But surely, you, who were so kind to me after my accident in the street, will you desert me now?" I argued. Her failure to give me any assurance that she was my friend struck me as peculiar. There was something extremely uncanny about the whole affair. I did not like it. "I have not said that I intend to leave you. Indeed, from motives of my own I have sought and found you; but before we go further I must obtain from you a distinct and faithful promise." "A promise--of what?" There was a brief silence, and I heard that she drew a deep breath as those do who are driven to desperation. "The situation is briefly this," the voice said, in a tone a trifle harsher than before. "I searched for you, and by a stroke of good fortune discovered where your unknown enemies had placed you, intending that at high tide you should be drowned, and your body carried out to sea, as others have been. From this place there is only one means of egress, and that being concealed, only death can come to you unless I assist you. You understand?" "Perfectly. This is a trap where a man may be drowned like a rat in a hole. The place is foetid with the black mud of the Thames." "Exactly," she answered. Then she added, "Now tell me, are you prepared to make a compact with me?" "A compact? Of what nature?" I inquired, much surprised. "It will, I fear, strike you as rather strange, nevertheless it is, I assure you, imperative. If I rescue you and give you back your life, it must be conditional that you accept my terms absolutely." "And what are those terms?" I inquired, amazed at this extraordinary speech of hers. "There are two conditions," she answered, after a slight pause. "The first is that you must undertake to make no statement whatever to the police regarding the events of last night."