Fletcher Reede, portrayed by Jim Carrey, is a high-powered lawyer who dedicates most of his time to his career, often neglecting his commitments as a father. He regularly prioritizes work over spending quality time with his young son, Max, leading to a pattern of dishonesty where he breaks promises to both Max and his ex-wife, Audrey, played by Maura Tierney. This behavior has caused Max to see Fletcher as someone who cannot be trusted.
In the midst of this strained relationship, Audrey begins dating Jerry, a hospital administrator who soon suggests they relocate to Boston for his new job. As Jerry proposes to Audrey, she struggles with the idea of uprooting Max, who is deeply connected to his father. During a precious day spent with his dad, Max witnesses Fletcher's dishonesty firsthand at the law firm, where Fletcher has taken on a new case under duress from his senior partner, Miranda. This adds to the burden of failing to meet the promise of attending Max's wrestling match.
The narrative takes a magical turn when Max, during a birthday celebration, makes a wish: "I wish that for just one day, Dad can't tell a lie." Strangely, this wish comes true, leaving Fletcher under a bizarre compulsion to be brutally honest about everything. He finds himself in one embarrassing situation after another, openly admitting thoughts he'd normally hide. From crass remarks about women to blunt truth bombs at the office, including confessing to his secretary, Greta, about his previous lies regarding her raise, Fletcher's life quickly spirals into chaos.
Now, with an upcoming court case involving his new client Samantha Cole, Fletcher grapples with the repercussions of his son's wish. Rather than lying to delay the proceedings, he must confront the truth, leading him to uncover a critical detail about Samantha’s marital agreements that ultimately enables him to win the case. Yet, this moment of triumph is overshadowed when Samantha exploits her newfound power, demanding custody of her children for additional financial support, which deeply unsettles Fletcher.
As tension mounts and Audrey contemplates moving with Jerry, Fletcher realizes that he must prioritize Max. In a desperate attempt to reconnect, he races against time, even to the extent of hijacking equipment at the airport to prevent their departure. In a disheveled but heartfelt moment, he swears to Max that he will be more present. Although Fletcher regains the ability to lie once more as the clock runs out, he finds that his brief experience of honesty has changed him for the better.
A year later, Fletcher and Audrey celebrate another birthday for Max. In a humorous twist, Max makes a wish while lighting the candles, only to find that his parents have rekindled their bond. As the family dynamic shifts back to a semblance of normality, they engage in playful antics, signaling a hopeful beginning as they chase each other around with a playful spirit. Fletcher's journey from professional dishonesty to familial reconnection is marked by the realization that honesty, while daunting, leads to heartfelt relationships.
