Necessary Doubt – Colin Wilson (1964)

Prof. Zweig believes his former pupil, Gustav Neumann, may be a dangerous criminal. It starts out as an exciting manhunt for someone who has presumably committed several murders & is about to embark on another. Yet the closer one gets to the supposed murderer, the less clear it is any murders have occurred at all.
“On Christmas Eve, while riding in a London hack, Prof. Karl Zweig sees a man he recognizes, getting into cab outside a hotel on Curzon St. He is so certain he goes immediately to call upon his friend Enid Grey, a retired Scotland Yard Inspector. If he is right he has spotted a dangerous murderer. For a time Necessary Doubt reads exactly like the best of the old-fashioned British thrillers. Then there begins to lurk in Zweig’s mind the disturbing suspicion that something is going on just beyond his comprehension; a conviction is growing that what he is experiencing is actually not reality at all, that just beneath the surface a whole new area of meaning is opening up. Yet the more convinced he becomes, the more startling is the depth & clarity of the picture which he finally begins to perceive, for however unorthodox its concept, it is every bit believable.”