"Yes," the low, booming voice caught the word. "The demon in you." The flaming eyes lifted. "Through some accident of inheritance, the dark blood is recessive in you, Clay. Physically, you appear quite human. Psychically, you are also, save for the shadow of strangeness that you feel, and for the waking of the demon when you fight. "But I'm afraid for you, Clay!" The terrible voice sank lower. "Passion will awake that slumbering demon. It will transmute that shadow into reality. You must walk with care, my son, or you will lose all humanity, in a hideous reversion to the dark blood! "If you married, you might become as monstrous as your brother. The strange blood was dominant in him. Tonight, in wishing to see you, he--or it--was displaying a fit of human emotion as rare as your fits of evil. For the most part, your twin is a mad monstrosity----" * * * * * "Tonight!" My mounting terror seized the word, and I reeled under an avalanche of dread. Icy sweat drenched me. Sick, quivering, I sank against the back of the chair. It was a little time before my lips could form the faint query: "Tonight? The thing in the cellar--that wanted me? That is my--my _brother_?" Doctor Kyle nodded. His dark eyes looked quickly away, as if with pity. His voice throbbed to me faintly through the gray mist of dread: "Your own brother, Clay. Its blood is your blood. Passion will cause your reversion to its form. What is equally dreadful, if you should marry Valyne, or any other woman, your children would probably be such things as it is!" The chill gloom of the musty attic chamber was spinning around me. Fainter, ever receding, still I heard the booming tones: "I attended your mother when you and your twin were born. I wanted to destroy the other, but neither she nor her father would allow. There was a strange perversity in her love. And Eliakim Coe desired the monster in the practise of the dark art that was overwhelming him. "As the strange being grew, your mother saw that it could never be reared in the world of men. When you were two years old--when Eliakim Coe died, a victim of the fearful powers he had summoned out of space--she left you in this household, and took the other into the forest. "Clay, it was a dreadful, secret life that your mother led, for the next twenty years and more, in these dark mountains above Creston! She sacrificed herself for her monstrous son. She kept it in a cave, on Blue Squaw Mountain. "She had no contact with the world, save for her infrequent midnight visits to me. But many a time, Clay, until the year when you left Creston, she stood beside your bed at night, and even touched your hair. But always she went back. "A few months ago she came to me, ill. I told her that she was going to die. On the last night of her life, she coaxed your strange brother down from the cave, and gave it into my keeping. Since then we have kept it in the cellar.