Live ants are coming to Room 2B, and Harry gets to take care of them when they arrive! As Ant Monitor, he'll be helping the teacher transfer all of the ants to their new home in the classroom where everyone can watch them.
But Harry's horrible ideas keep getting him into trouble. So what if he happened to put the ants right on top of Mrs. Foxworth's container of yogurt? Fortunately, when a few of the ants manage to escape, Horrible Harry knows exactly what to do.
But then a very sad accident occurs in the classroom fishtank, and Harry feels terrible -- even though it's not his fault. As Room 2B finds out, some ideas can be too horrible.