I need to find a short novel/book (less than 100 pages) by one of .. (not short stories)?

As some already noted, your single best bet is Metamorphosis, by Kafka. Also, Kafka's some what shorter work In The Penal Colony, around 50 pages depending on page size, is superb. Also worth a try are Captain Burle by Zola, Raise High the Roof Beam Carpenters by Salinger and The Gambler or Notes From Underground by Dostoevsky.l Faulkner's The Bear is superb, but a dense and difficult read in spite of short length. His Wild Horses, actually a section of his novel The Hamlet, stands well on its own and is easier to read.