Nereid tied our little craft to a metal fastener against the black, sleek rock-cliff. Then for me she produced the air-mechanisms and round transparent helmet with elastic gasket to fit around my throat. And heavy, metal-weighted shoes for us both. But no helmet was needed for her. "We will be there in ten or fifteen minutes," she said. "I can see better without the head-covering." We dropped into the luminous, opalescent water. Nereid held my hand as I floundered a little, trying to remain balanced upright while our weighted shoes carried us slowly down. It was a descent of some fifty feet, with the opalescent surface light fading into the black-green of the depths. Then slowly an undulating dark surface seemed coming up to us; and we landed, swaying on our feet. Weird, submarine world. The jagged slope to one side went on down into the depths. Beside us, swaying leafy vegetation stood upright in the water--a little thicket here, with what seemed a rocky path, ascending along the edge of the black abyss. Through my transparent helmet I stared at Nereid. She was smiling, unbreathing, as much at home down here as on the land. She gestured that we were to take the ascending path; and held my hand to steady me as we started our swaying, shoving climb. I could see now that ahead of us there was a little tunnel into the cliff where we would emerge into air. And suddenly I felt Nereid's hand tighten convulsively on mine. I saw the blurred figures in another second, two upright swaying blobs close ahead of us as we emerged past the seaweed clump. Two men down here. Tollgamo's men? I shook loose from Nereid and plunged forward. Then in another second I could see the faces in the transparent helmets. And one of them I recognized. It was Leh and Allen here, as startled as ourselves at the sudden encounter. * * * * * I think now I need only briefly sketch that following hour or two while within the Arsenal fortress Allen and I met Peters and his men, and all of us hastily prepared for Tollgamo's attack. I found Nereid's father quite what I had expected--a quiet, grave-faced man of somewhat my own type, garbed like his fellow scientists in tight trousers and blouse of sleek black fabric. There was no time then to exchange more than the briefest of questions, as Nereid hastily told him what had happened to her since her little note had informed him of her furtive departure for Earth. "You worried me very much, my daughter," he said quietly. And the same sense of humor which she herself had twinkled now in his grey eyes. "But I think this is no time for reproof."