A tough and seasoned police detective is given an undercover assignment to find and protect a key witness for a major case involving a notorious drug dealer. The catch – the witness is the estranged wife of the criminal, who's gone into hiding, and the only lead to her whereabouts is the location of her young son. The detective must assume the identity of a kindergarten teacher in a small Oregon school to get close to the boy and gather information. With zero experience in teaching or handling children, the detective has to adapt quickly to the chaotic world of five-year-olds, all while keeping his true mission a secret.

As the detective struggles with his rambunctious classroom, he begins to form a bond with the children and develops a romantic interest in another teacher who is also the mother of his key witness-kid. These connections lead him to not only become a better law enforcement officer but also start to shape him into a more sensitive and caring individual. Meanwhile, his police partner is conducting parallel investigations and often steps in with support and cover. What was initially seen as just another assignment slowly turns into a personal journey, amidst humorous child-related escapades and the contrasting realities of his two worlds – crime and crayons.