Mrs. Grunion is first introduced when Mr. Peabody is meeting with the principal about Sherman biting Penny the lunch room. She walks out of an office in the side of the Principal's office. She is shown to have more power over the principal and is determined to have the adoption agency reclaim Sherman from Mr. Peabody.
Later on, after she did try to take Sherman away, Mr. Peabody's fatherly instinct got the best of him and he decided to bite her arm. Ms. Grunion called the police to have him taken away to the pound. Shortly thereafter, a hole was ripped in the space-time continuum when Sherman and Mr. Peabody returned independently to when they were already in the present, resulting in two of each person. Peabody and Sherman fix the hole, but Grunion proclaims that one day Mr. Peabody will make a wrong move and that then, she will get him. Agamemmon grabs her as he is taken back to his time, taking her as well. In a post-credits scene, she is last seen marrying Agammemmon.
Mrs. Grunion is a corrupt social worker that is attempting to get Sherman taken away from Mr. Peabody. However, she does not acutally care for Sherman's well being, she actually wants to ruin Sherman's and Mr. Peabody's lives and make them miserable. She even went to as far as reporting Peabody to the police with a false accusation, just so she can have him put down.
Ms. Grunion is fat and has black hair. She wears a pink suit.
- Grunion's voice actress Allison Janney also voiced Gladys Sharp, one of the main antagonists in Over the Hedge, another film by DreamWorks Animation.
- The character's illustration bears a striking resemblance to actress Marcia Gay Harden in a fat suit.
- She probably does not want Peabody to have Sherman because she hates dogs.
- If you know anything about Greek mythology, Grunion might have been killed, because when Agamemnon brings home his new wife...his old one won't take it very well.
- Given her actions and downright evil ways, Grunion is easily the most evil villain in the whole Rocky and Bullwinkle franchise and the Jay Ward franchise in general.