"The Mysterious Stranger" is a very odd story. Satan (or, at least his minion nephew, a surrogate dark angel as presented here) is more or less the hero; humankind and religion come in for a deserved blistering drubbing for the race's cruelty, ignorance and hypocrisy. The story takes place in Austria in 1590; it's told from the viewpoint of a boy (actually a grown man reminiscing), who along with his friends are dazzled by and befriended by Satan; they come to realize that Satan is more an observer and agent than a purposely malicious being - sort of the way predators are in the wild. It is only man who preaches morality and in the same breath commits malicious, sadistic cruelty with relish.