A man is shot in broad daylight from a long distance outside Missoula, Montana. The local detectives connect the shooting with another unsolved killing in Munich, Germany. FBI agent Denise Marceau and Missoula detectives Doug Mills and Sam Caffey seek the support of Alexander Granger, agent of the German Federal Police (BKA). They join forces to uncover the mystery behind the shootings while further people are being killed. The chase for the killer leads Denise Marceau and Alexander Granger across the west of the USA unearthing a long-forgotten tragedy. The shooter has a score to settle with the people that took away his family unraveling the DEPTH OF THE PAIN.