Mrs. Mercutrode is a middle-grade novel about a substitute teacher known for her unique teaching methods and creative discipline. The students are in for the education of a lifetime when Mrs. Mercutrode arrives with a magic disappearing wand, an antique collection of jazz records, and a tank full of exotic insects and rodents from all of her world travels.

When the parents try to have her fired, she convinces them she should stay after delivering a rousing speech and preparing an extraordinary feast of culinary delights. The next day, however, the children notice that some of the insects and rodents are missing from the tank.

Mrs. Mercutrode introduces the children to the joys of literature by dressing up and playing the part when studying everything from pioneers to the Roaring Twenties. When the annual essay contest begins, Mrs. Mercutrode works the students until their fingers are limp and they think their brains will melt, but the results are incredible. The students are disappointed when they don't win the contest, but a strange turn of events results in Mercutrode's class winning first prize.