Charlie Baileygates (JIM CARREY) is a seventeen-year veteran of the Rhode Island police force. Mild-mannered to the point of repeatedly being ignored and/or taken advantage of, the motorcycle cop stoically accepts the many indignities thrown his way, the most major being when his wife, Layla (TRAYLOR HOWARD), runs off with a dwarf limo driver (TONY COX) after he fathered their three African-American boys.
With the years passing, those boys -- Jamaal (ANTHONY ANDERSON), Lee Harvey (MONGO BROWNLEE) and Shonté Jr. (JEROD MIXON) - have grown into well-educated, but foul-mouthed young men who love and respect their dad. Unfortunately, no one else in their town does and after receiving one too many affronts thrown his way, Charlie finally snaps. As a result, his psychologically deranged alter ego, Hank (JIM CARREY) emerges as a vengeful cop determined to offer a lot of payback to those who were previously disrespectful to him.
Diagnosed and medicated for a case of advanced delusional schizophrenia with involuntary narcissistic rage, Charlie is assigned by his superior, Colonel Partington (ROBERT FORSTER), to escort the indignant and ticked off Irene (RENEE ZELLWEGER) back to upstate New York where she's to face questions about her knowledge and involvement in fraud and embezzlement committed by her boss and possible former lover, Dickie Thurman (DANIEL GREENE).
Once Charlie delivers Irene to local cop Lt. Gerke (CHRIS COOPER) and federal agent Boshane (RICHARD JENKINS), he thinks his assignment is complete. When someone later kills Boshane's partner while looking for Irene, however, he's suddenly pulled back into the case. Hitting the road to protect her but forgetting his pills, Charlie tries delivering her one more time to Gerke, but after a close call involving him and the suddenly reemerged Hank, they decide they must stay on the road and out of sight.
As such, and after picking up an albino waiter, Whitey (MICHAEL BOWMAN), Charlie and Irene try to figure out what's going on and save her from danger. With the police, federal agents and Charlie's three sons all looking for him, the improbable road trio tries to solve their dilemma, all while dealing with repeated appearances by Hank who's prepared to take on anyone or anything in his way.