After years of pursuing infamous drug dealer Cullen Crisp, LAPD Detective John Kimble arrests him for murder. He receives the whereabouts of his ex-wife, Rachel Myatt
   Crisp, who allegedly stole millions from him before fleeing with their son, Cullen Jr. Partnered with former teacher-turned-detective Phoebe O'Hara, he goes undercover
   in Astoria, Oregon to find Rachel and offer her immunity in exchange for testifying against Crisp. O'Hara must act as a substitute teacher in Cullen Jr's kindergarten class
   at Astoria Elementary School. O'Hara falls ill with a terrible case of stomach flu, so Kimble takes her place. The suspicious school principal, Miss Schlowski, is convinced
   he will not last long before quitting. Though initially overwhelmed, he adapts to his new status quickly, despite not having any formal teaching experience. With the use
   of the class mascot, positive reinforcement, his police training as a model for structure in class and his experience as a father, he becomes an admired and cherished
   figure to the students. He begins to enjoy his undercover role. At one point, he deals with a case of child abuse, winning Miss Schlowski's favor. In observation of his
   teaching style, she assures him that she does not agree with his methods, but can tell he is a good teacher. Kimble also becomes fond of fellow teacher Joyce Palmieri,
   whose son Dominic is one of his students. She is estranged from her husband and will not speak of him, telling Dominic that he lives in France. Conversing with the
   gradually more trusting Joyce, Kimble deduces that she is Rachel and that Dominic is Cullen Jr. Back in California, the case holding Crisp in jail is closed after the witness
dies from using tainted cocaine provided by Crisp's mother, Eleanor. He is subsequently released from prison, and quickly travels to Astoria with Eleanor to search for Cullen Jr.

When Kimble learns Crisp has been released, he confronts Rachel about her identity, saying he can protect her if she cooperates. Outraged that he misled her, she tells him that Crisp lied about her stealing the money to convince drug dealers to help him find her; the real reason was to find Cullen Jr, as he was angry that Rachel disappeared with him (even though she had every reason to do this, given her ex-husband's infamy, and the bad example of a father he would be as a result). Crisp starts a fire in the library as a distraction to kidnap Cullen Jr, but uses him as a hostage when Kimble arrives. Kimble's ferret, who was hiding in Cullen Jr's shirt, bites Crisp in the neck, allowing Cullen Jr to escape; Crisp shoots Kimble in the leg before Kimble fatally shoots Crisp. Outside, Eleanor injures O'Hara with her car before going inside and discovering Crisp dead; she wounds Kimble in the shoulder, but O'Hara appears and vengefully knocks her unconscious with a baseball bat. Eleanor is then arrested and the unconscious Kimble is hospitalized with O'Hara, with both of them making a full recovery. O'Hara returns to the police force in Los Angeles, while Kimble decides to retire, staying in Astoria to become a kindergarten teacher at the school full-time. Rachel joins him and the two share a kiss while everyone cheers.