Calvin tries to earn money to buy Stella, the babysitter, a present for her sixteenth birthday because he feels guilty for taking advantage of her allergy to cats.

When Calvin gets a school assignment to do some original research, he decides to investigate his dog's stinky breath and ends up learning about more than just smells.

Fourth-grader Cal learns a lot about teasing and standing up for others when a weird new student joins his class, while Stella, the tenth-grader who lives with Cal's family to help his mother, practices for her driving test.