Alan E. Nourse 
The Dark Door [EPUB ebook] 
With linked Table of Contents

It was almost dark when he awoke, and lay on the bed, motionless and trembling, his heart sinking in the knowledge that he should never have slept. For almost half a minute, eyes wide with fear, he lay in the silence of the gloomy room, straining to hear some sound, some indication of their presence. But the only sound was the barely audible hum of his wrist watch and the dismal splatter of raindrops on the cobbled street outside. There was no sound to feed his fear, yet he knew then, without a flicker of doubt, that they were going to kill him.