Mr. Peabody is a gifted anthropomorphic dog who has an adopted 7-year-old human son, Sherman. He tutors Sherman travelling throughout history using the WABAC, a time machine. They visit Marie Antoinette in Versailles during the French Revolution in 1789. Getting caught in the Reign of Terror, Peabody is nearly sent to the guillotine by Maximilien Robespierre, but escapes with Sherman through the Paris sewers.
In the present day, Sherman attends the Susan B. Anthony School in New York City. His knowledge of the apocryphal nature of the George Washington cherry-tree anecdote leads to a fight with Penny Peterson in the cafeteria where she puts him in a choke hold. Peabody is called in by Principal Purdy who tells Peabody that Sherman had bit Penny. He is also confronted during this meeting by Ms. Grunion, a Child Protective Services agent, who implies that Sherman's behavior is due to being raised by a dog. She informs Peabody that she will come to their home to investigate whether he is an unfit parent.