A sixty-nine-year-old man with no children is a high school biology and astronomy teacher. He recently had a heart attack and can no longer physically exert himself. However, his wife is in such great shape that she is away for weeks, hiking the Appalachian Trail. While his wife is away, the man realizes his centuries-old elm tree has become infested with vermin. The man's neighbor, Mr. Pike, who owns a construction company and is notorious for using the cheapest pipes he can, though they do not last, notices the infestation. Mr. Pike comes over to the man's house and offers to cut down the man's tree, saying that the tree will die and fall on his house and that his own young elms will become infected. However, the teacher is sentimental about the tree and knows there is a slight chance it will not die. He refuses Mr. Pike's offer and puts pesticides along the tree, though he has been told it will not work. To his and Mr. Pike's surprise, the bugs disappear.

The man reflects on the wildfires that struck his town one summer as a young boy. His pharmacist father tracked the wind patterns and path of the fires to alert the neighborhood when or if conditions became so dangerous that they had to leave their homes. One day, the man's father predicted danger and told everyone to evacuate. The man's mother, however, loved her home and refused to leave it. The whole family left without her, and their home ended up not being in the path of the fires. The man thinks about how passionate and stubborn he is about their house and decides he will be the same way about his elm.

When the bugs return to the tree, Mr. Pike tells the man that he has reported the situation to the authorities. The man decides to do what he must: infect Mr. Pike's elms, which will probably live even if infested so that Mr. Pike will no longer want to chop his elm down. The man takes a jar of the bugs to Mr. Pike's house and hides in his cellar, waiting to place them. As he is hiding, the man sees Mr. Pike take his son Kurt outside and show him the constellations, though Mr. Pike makes up all the names. Then, the two go inside and watch TV together, with Mr. Pike occasionally rubbing Kurt's hair. After watching the two, the man decides he cannot infect Mr. Pike's tree. He goes home and is unable to sleep. When the newspaper delivery boy, one of the man's former students, arrives the following day, the man tells him to look up at the stars.