That night, however, a blow fell upon me. An incident which I had constantly dreaded occurred, for by the last post was delivered one of those strange typewritten mandates from the unknown. The envelope was a blue-grey one, such as lawyers use, and the postmark showed that it had been dispatched from the Lombard Street office, in the City. I tore it open in fear and trepidation, and glanced at the few even lines it contained. The lines I read were signed by the word "Avel," traced with a heavy hand in rough Roman capitals, and were as follows:-- "To-morrow, the fourteenth of October, enter the Park at Grosvenor Gate at four o'clock, and wait at the third seat on the path which leads to the band-stand." I stood silent, with the mysterious missive in my hand. Some secret service was evidently required of me. The shadow of that fateful night had again fallen, crushing me beneath its weight of mystery and crime. I thought of the unknown Edna, and pictured her in comparison with Mabel. In my helplessness I had become an unwilling tool in the hands of the former, and now I hated and despised her. This galling servitude which she had imposed upon me under penalty of death was doubly irksome now that I loved; yet so mysterious and tragic were all the circumstances that I feared to break the bond that I had given. In ordinary circumstances I think I should have been eager to obey this sudden demand to go to the Park on the following day. There was a distinct air of adventure in the appointment, and, eager to fathom the mystery surrounding Edna, I saw that this meeting might furnish me with some clue. But I recollected Mabel, all sweetness and purity, and hated it all. Edna had declared that she herself was not the mysterious "Avel," yet I had no reason to disbelieve her statement. To me it seemed as though she were acting under instructions which had for their object the preservation of the secret of the midnight crime. Who was the young man who had fallen victim? His identity puzzled me always, until the problem had become so perplexing as to drive me to despair. Although time after time I had searched the newspapers, I had found no one answering to his description mentioned as missing. He had evidently been done to death and his body disposed of without a single inquiry, while the crime had been concealed with an ingenuity which appalled me. Might I, myself, not fall victim in a similar manner if I refused to obey these strange mandates of an unknown hand? These thoughts were the reverse of reassuring, for even if I went to the police they would be unable to assist me. A detective might keep the appointment in the Park, but it was certain on seeing a stranger in the vicinity the person who intended to meet me would give him a very wide berth.