Split Infinity is the first book of the Apprentice Adept series. Piers Anthony is best known for his Xanth series, but I enjoyed the first three novels of this series as much as I did anything else that Piers Anthony wrote. The novel (and series) deals with a dual world. Proton is a science fiction orientated world. The laws of science rule the world. The planet is desolate with the air being unbreatheable. People live in large city sized domes. People are divided into two classes. Citizens are extremely wealthy, are permitted to wear clothing, and are the rulers of Proton. Serfs do the work, are not permitted clothing (though are permitted their own diversions as long as it does not interfere with their work), and have a limited tenure on Proton. After their tenure expires, they must leave the planet (though they do get to collect a large amount of their earnings at the end of tenure). Phaze is a fantasy world where magic exists and the world is still fairly pristine. The powers of Phaze are human magician called Adepts (they are adept in one particular facet of the magic). Dragons, unicorns, and werewolves are real. The features of the Phaze are the same as Proton, except the land hasn't been ruined.
The protagonist of the novel is a man named Stile. Stile is a serf on Proton. He is a jockey for a Citizen, but in the private world of the serfs, he is a master at the Games. The Games are the main entertainment for serfs, and they get to test their skills at various sports/games/arts/activities. A master player can excel in most facets of the Game. Stile is a master player and is two years from the end of his tenure. He meets a female robot named Sheen (get the pun?). Robots on Proton, depending how they are programmed and assembled, can look, sound, feel, and touch exactly like a human. Sheen is such a robot. Sheen warns Stile that someone is trying to kill him. Her job is to protect him. Over the course of the novel, we see attempts on Stile's life and he accidently crosses a "curtain" to the magical world of Phaze. In Phaze, Stile meets a unicorn and a werewolf who will kill him if he uses magic. He is the image of a murdered Adept from Phaze, and he has the abilities of an Adept. Someone is still trying to kill him in Phaze. The novel is the beginnings of his quest to find out whom, and also to discover his own identity in Phaze.
This was one of my favorite fantasy novels when I first started reading in the genre back in high school. My favorite part of the novel was the aspect of the Games on Proton. I thought it was a wonderful idea and it was what hooked me on the books. It has been nearly ten years since I've last read any of this series, and while my taste and somewhat matured and the material is not as fresh as it once was, this is still a wonderful series and is a lot of fun to read. For any fan of Xanth or of Piers Anthony, this one needs to be read.