It is also revealed that Mr. Peabody has invented a time machine, WABAC, which is pronounced, "way back". He uses this machine to educate his son, through first-hand experience about historical events that happened over the years.
But trouble begins when Sherman starts attending school. Though he is bright and brilliant, he is taunted by a spiteful intimidator, Penny Paterson (Ariel Winter). In retaliation to the bullying, he bites her. The matter escalates. The parents are called and a social worker, Miss Gruinion (Allison Janney) is put on the case.
The inciting moment of the film turns out when Miss Gruinion questions, "What kind of a father can a dog be to a boy?"
Rude and obtuse, she pursues the case with the intention of withdrawing all parental rights from Mr. Peabody.
In order to smooth things out, Mr. Peabody invites Penny and her parents (Leslie Mann and Stephen Colbert) for dinner. While Mr. Peabody engages with the parents, he lets Sherman iron out his differences with Penny.
In a moment of one-upmanship, Sherman disobeys his dad and uses the WABAC to prove his point of how he knows that George Washington never chopped down a cherry tree.
What follows is a series of adventures through history, that starts in ancient Egypt with Penny getting betrothed to nine-year-old tyrant King Tut (Zach Callison), and carries on through encounters with Leonardo Da Vinci (Stanley Tucci), and Agamemnon (Patrick Warburton) on the eve of the sacking of Troy, and the Marie Antoinette sequence amongst others.
