Imagine a world in which classes are divided not by wealth or religion but by how much each group can remember. Monos, the majority, have only one day's worth of memory; elite Duos have two. In this stratified society, where Monos are excluded from holding high office and demanding jobs, Claire and Mark are a rare mixed marriage, a shining example of a new vision of tolerance and equality. Until a beautiful woman is found dead. The woman is Mark's mistress, and he is the prime suspect in her murder. The detective investigating the case has secrets of his own. So did the victim. And when both the investigator's and the suspect's memories are constantly erased, how can anyone learn the truth?