Classic Andre Norton-- a cross between fantasy and science fiction.
Start with a snippet of Charles Fort missing persons stories, throw in some alternate worlds, add a little Arthurian myth and sprinkle with enigmatic alien killers. Drop two young adults into this mix, dusted with a cat and dog of strange intelligence, and this noted author comes up with HERE ABIDE MONSTERS.
a nice book, with a landbound "Bermuda Triangle" location and what happens to those who are caught by the effect. Andre's stories are usually fast paced and lively. Would be a good read for anyone with, say, a grade 8 and above reading ability.