Tom is diagnosed with atrial septal defect at 4 years old, a terminal illness that is essentially 'a hole in the heart'. He is told that his life expectancy is the age of 16, or if he's lucky, maybe 18. As he grows up, his mother restricts him from the outside world, forbidding him from excitement out of fear of worsening his condition. Tom is homeschooled, only leaves his room for food or to do chores, and is completely cut off from other kids his age. He struggles with anxiety of the outside world but also anxiety of his approaching death. One day, he meets Ruby, who is extremely adventurous and begins helping him explore his surroundings. They have lots of fun and she essentially shows Tom the meaning of life. As they grow older, they lose touch and Tom goes back to living his ordinary routine life with no excitement. He reaches out to Ruby in search of the excitement he once knew, and they meet up, where he discovers she now has a son. They catch up, but ultimately, Tom decides to go back to living a longer life instead of a shorter, but fuller, life.