At the start of this exemplary psychological thriller from Walker (The Night Before), guilt-ridden Molly Clarke runs out of gas in Hastings, Conn., fives years to the day after the death of her younger daughter, Annie, for which she blames herself. She gets out of her car and starts walking, but never reaches home. Two days later, the Hastings police find a handwritten note Molly left in a hotel room asking her family not to look for her. Two weeks later, 21-year-old Nicole, Molly's older daughter, receives a tip from a woman who claims she saw Molly the day she disappeared getting into a stranger's pickup truck. Despite the strained relationship between Nicole and Molly since Annie's death, Nicole decides to investigate. When she learns of another woman who vanished from Hastings, she tries to determine whether the two disappearances are connected. Chapters from Molly's perspective that reveal her present whereabouts heighten the tension. Distinctive, well-developed characters complement the skillfully paced plot. This moving look at the bond between a mother and her children reinforces Walker's place at the top of the genre. 75,000-copy announced first printing. Agent: Wendy Sherman, Wendy Sherman Assoc. Literary Management. (Sept.)