A brilliant dog named Mr. Peabody adopts a young boy, Sherman, and raises him through extraordinary adventures facilitated by the WABAC machine, a time-traveling device. Their bond is tested when Sherman starts school and encounters challenges with his classmate, Penny Peterson. After an altercation leads to a parent-teacher meeting, Mr. Peabody invites Penny and her parents over to mediate. However, things take a drastic turn when Sherman defies Mr. Peabody’s instructions and uses the WABAC to impress Penny, transporting them to ancient Egypt.

In their attempt to return home, the trio travels through various historical eras, encountering figures like Leonardo da Vinci and King Tutankhamun. Each adventure underscores the importance of trust, responsibility, and friendship. As the fabric of time begins to unravel due to their actions, Mr. Peabody and Sherman must work together to rectify their mistakes and ensure history remains intact. The duo's journey not only dives into the past but also strengthens their familial bond, highlighting the universal themes of love and growth.