Sleator incorporates the new theories about chaos and its generation into this dark, complex SF story. Max awakes one morning to discover that he's lost a day. Furthermore, a brilliant scientist named Sylvan and his glamorous daughter, Eve, are after him to return something he doesn't remember taking. Even more confusing, Max meets a second, less colorful Sylvan and Eve who also want something from him. From various hints and clues, Max assembles an explanation: the missing instrument is a "phaser," a hand-held time machine. Using it to change the past inevitably remits in a bifurcation of time lines and a chaotic, lawless universe--as the first Sylvan and Eve have ruthlessly proven in their own time line. Now refugees, they must eliminate the other pair before they can settle here. Amid a welter of treachery, half-truths, second thoughts, and brisk zipping through time, Max foils the bad guys and ends up working in the lab with the more cautious Sylvan, while building his own phaser on the sly. To Max, Eve and the phaser are like drugs; though he knows both are deadly (she has matter-of-factly killed her unstable father), he just can't keep his hands off either. Max may initially enlist reader sympathy, but he's a sneaky, vacillating character, unable to resist his baser urges. Like The Boy Who Reversed Himself (1986), the story here is less memorable than the science behind it.