William Sleator is noted for his popular and suspenseful science fiction and fantasy for young adults. And like many of his other books, The Duplicate is fast paced and exciting. Although it is somehwat formulaic, the book raises interesting issues about the importance of and the need to maintain one's individual identity. This theme is played out by the book's main character, David, through his reactions to two duplicates of himself, and the increasing tension fo the last few chapters helps to raise the book above mere formula fiction. With this novel, Sleator also adds to a large body of fantasy fiction that deals with doppelgangers, or evil doubles.