Nine-year-old Calvin catches the attention of the school bully on the day before he starts fourth grade, while at home, the unfriendly, fifteen-year-old daughter of his mother's best friend has taken over his room.
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 his teacher asks him to write a persuasive argument about something he really wants, fourth-grader Calvin creates a unique way to express his desire for a dog.
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.
Fourth-grader Calvin flies from Oahu to the big island of Hawaii to go on a deep-sea fishing trip with Ledward, his mother's boyfriend, and learns to appreciate other living creatures-- especially one enormous marlin.
