Velocity by Dean R. Koontz

A small-town bartender finds a chilling note on his car: report it to the police and an older charity worker will die, ignore it and a beloved teacher will be killed. Each day brings a new ultimatum, pushing him into a high-speed cat-and-mouse game with a sadistic mastermind who seems to anticipate his every move. As bodies fall and suspicion turns toward him, he races to decipher the taunts, protect his comatose fiancée, and confront the terrifying moral calculus of choices made under relentless time pressure.

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