Sarah and Rex are kidnapped by an old enemy - criminal mastermind Rupert Mankiewicz. Mankiewicz's mission is to exact revenge by weaponizing Rex. Mark and Jesse launch a desperate investigation to find them before Mankiewicz can fulfill his deadly mission.
Detective Charlie Hudson, a cunning Major Crimes detective for the St. John's Police Department, teams up with an unusual partner - Rex, a former-K9 German Shepherd, whose heightened senses keep Charlie hot on the trail of his suspects. Together, they investigate puzzling crimes, from a kidnapping which reveals a much larger conspiracy at play to an art theft cuddle which runs deep into the world of high society. With Charlie's deft detective work and Rex's keen canine senses, this crime-fighting pair is unstoppable.