Eighty-six-year-old Irving Zisman's moment of relief following the passing of his wife, Ellie, takes a chaotic turn when he unexpectedly finds himself responsible for his eight-year-old grandson, Billy. This predicament arises after Billy's mother, Kimmie (Irving's daughter), lands back in jail due to a parole violation. Kimmie pleads with Irving to ensure that Billy reaches his father safely. Following a video call with Billy's unreliable dad, Chuck, who instructs them to make it to Raleigh, North Carolina by 2 P.M. on Sunday, Irving and Billy embark on their wild journey.
In a bid to gather some cash, Irving sells off his late wife's possessions and, with the help of two men, manages to stow Ellie's body in the trunk of his car. With the road ahead of them, they set off, but not before stopping at a local market where Irving attempts to charm a woman while Billy fumbles with a malfunctioning ride. As a result of his frustration, Irving inadvertently launches the ride off its base.
When Billy's hunger strikes again, Irving hatches an ill-fated plan to ship him off via the post office, which quickly goes awry. They then find themselves at a Bingo event, leading to an array of humorous antics as Billy searches for a surrogate dad among the crowd.
Their escapades continue at a supermarket where Irving shoplifts food, crafting sandwiches for both himself and Billy before narrowly escaping the store's staff. The duo then checks into a motel, where Irving finds himself at a male strip club seeking companionship. His unintentional exposure creates quite the stir, much to the horror of the spectators.
As they near their destination, Irving tries using Billy to attract women yet fails to make any connections. Stopping at a diner, their mischief escalates when Irving crashes into a massive penguin statue, angering a diner promoter who insists he fix the mess. In their typical boisterous fashion, they turn their time at the diner into a competition of who can make the loudest flatulence sounds, but things take a turn for the worse when Irving accidentally defecates on the wall, prompting their hasty exit.
Hunger knocks again, and they attempt to infiltrate a wedding reception at a church. Just as Irving swipes a glass of champagne from a precariously stacked tower, disaster strikes as the entire structure collapses. His unfortunate timing leads to further chaos when he lands atop the wedding cake during a group photo.
They finally make their way to a bar, where they are to meet Chuck. Upon arrival, Irving witnesses Chuck's poor parenting skills and the intervention of the Guardians of the Children, an organization dedicated to protecting abused children. With a sudden change of heart, Irving rushes back to rescue Billy from Chuck, evading disastrous parenting.
In a final celebration of their bond, Irving and Billy decide to crash a beauty pageant after spotting a flyer during their travels. Their adventures culminate as they reach a bridge where they solemnly dispose of Ellie's body into a river, then proceed to enjoy a peaceful day of fishing together.
