Walter Black (Gibson) is a depressed CEO of Jerry Co., a toy company nearing bankruptcy. He is kicked out by his wife (Foster), to the relief of their elder son Porter (Anton Yelchin). Walter moves into a hotel. After unsuccessful suicide attempts, he develops an alternate personality represented by a beaver hand puppet found in the trash. He wears the puppet constantly, communicating solely by speaking as the beaver, helping him to recover. He reestablishes a bond with his younger son Henry and then with his wife, although not with his elder son, Porter. He also becomes successful again at work by creating a line of Mr. Beaver Building Kits for kids.
Porter, who gets paid to write papers for schoolmates, is asked by Norah (Jennifer Lawrence) to write her graduation speech. He gets emotionally attached to Norah but his father's actions with the beaver puppet embarrass him.
Walter's wife moves out of the house with the children, because he lied to her about the puppet being part of a treatment plan monitored by his psychiatrist. She feels she can no longer communicate with her husband and that he is suffering from a dissociative identity disorder, with the beaver taking him over.
Part of Walter's personality realizes what he has put his family through and wants to get rid of the beaver to get back together with his family, but the beaver resists. Walter finally takes the puppet out of his life by cutting off his arm at the elbow. He gets a prosthetic hand and is placed in a psychiatric hospital.
Norah reconnects with Porter. She starts the speech he wrote, but stops and admits publicly that she did not write it herself. She switches to explain the value of truth and her trauma caused by her brother's death some years ago. Porter realizes the value of his father and reunites with him.
Walter Black becomes himself again and returns to a normal life.Cast