Saturday, Memorial Day weekend, May 23rd. In the small town of Promise Falls, New York, hundreds of people are going to the hospital with similar flu-like symptoms, dozens have died. Investigators quickly zero in on the water supply. Cal Weaver wonders: who would benefit from poisoning the town? Meanwhile, Detective Barry Duckworth recognizes the killer's handiwork in the murder of a college student. All the strange things that have happened in the last month start to add up... the motive for harming the people of Promise Falls points to the number 23.