It's the night of the full Cold Moon - the month of December according to the lunar calendar. A young man is found dead in lower Manhattan, the first in a series of victims of a man calling himself the Watchmaker. This killer's obsession with time drives him to plan the murders with the precision of fine timepieces, and the victims die prolonged deaths while an eerie clock ticks away their last minutes on earth. Lincoln Rhyme, Amelia Sachs and the rest of the crew are tapped to handle the case and stop the Watchmaker and his partner, Vincent Reynolds, a repulsive character with a special interest in the female victims of the killer. Amelia is not only Lincoln's eyes and ears at crime scenes on the Watchmaker case, but she's now running her own homicide investigation - her first case as lead detective. The policewoman's unwavering efforts in pursuing the killers of a businessman, who left behind a wife and son, sets into motion clockwork gears of its own, with consequences reaching to people and events that will endanger not only many lives but Lincoln's and Amelia's future together.