After accidentally stealing from a grocery store due to having trouble with the self-checkouts and causing a scene with the store manager, recently widowed Ed Marino (Robert De Niro) is visited by his daughter Sally Marino-Decker (Uma Thurman), who wants him to move in with her family. Ed does not want to leave his house because he built it all by himself. Sally convinces Ed to move in with her nonetheless, and gives him her son Peter’s (Oakes Fegley) bedroom. Peter is not happy about giving his room to his grandfather and being moved to the attic. Ed is welcomed by Sally’s husband Arthur (Rob Riggle) and two daughters, Mia (Laura Marano) and Jenny (Poppy Gagnon). During his first day moved in, Ed spends most of his time in his new room, sitting in his chair and looking at the sky, still thinking about his late wife.The War with Grandpa
Peter then tells his friends Billy (Juliocesar Chavez), Steve (Isaac Kragten) and Emma (T.J. McGibbon) about his grandfather moving in with his family and living in his room. After a miserable first night in his new room, Peter decides to declare war. Ed agrees to war, as long as they follow the agreed upon rules of engagement: they cannot damage other people’s belongings and cannot tell the family about this. Peter pulls a series of pranks, including replacing Ed’s shaving cream with quick-drying foam and damaging his record player. Ed gets back at Peter with pranks including removing the screws from all of Peter’s furniture and rewriting his school report. Ed turns to his friends Danny (Cheech Marin) and Jerry (Christopher Walken) for some advice. Over time, Ed begins to spend time with his granddaughters and son-in-law and learns how to use modern technology, such as self-checkouts and apps.