Clare Frayn was giving her brother a ride home, on the night someone ran in front of her car and caused the accident. Her brother died instantly. Funny thing was, they never found his arm. Funnier than that - though Clare isn't laughing - is that the man who ran in front of her car seemed to be disappearing around a corner shortly after the accident, carrying something looking suspiciously like an arm...
A couple of months later, popular exploitative true-crime writer Edmund Hall contacts Clare for help in researching his latest book, "Satan's Cannibal," about the man he is certain was responsible for Clare's brother's death. When a young boy, Hall went to school in Clare's Liverpool neighborhood with a creepy kid named Christopher Kelly. Kelly was a ghoul, who eagerly attacked and ate living small animals - and even badly scared the school bully, by nearly biting off his nose.
Clare and Edmund play amateur detective, with a few friends, to track Kelly down. Of course, with that much attention coming his way, it can't be too long before Kelly turns the tables, and comes looking for them...
This was Ramsey Campbell's first novel, and it still reads quite well. It's more a crime story than anything else, sort of an odd and eerie "day in the life" of an unsettled and unsettling shadow-crawler of a man. Balancing the psychological and possible supernatural aspects is what makes Campbell's story so compelling - that, and his fascinating characterization of a truly bizarre criminal.
The book reads like a good episode of The Alfred Hitchcock Hour, and is surprisingly mature for this kind of material. It may well have partly inspired Thomas Harris' more famous Hannibal Lecter novels, Red Dragon especially - though it isn't quite as good, just along similar lines.