Henry Smith is a student at a college prep school whose parents are well-off. Because of his love for his son, Henry's father attempts to protect Henry from life, often spending money to that effect, but of course, this doesn't stop life from afflicting Henry. One day, Franklin, Henry's older brother, gets hit by a car and hospitalized. The novel's action begins when Franklin arises from his coma, looks Henry straight in the eyes, mutters a single word, "Katahdin," and then dies.
This is when the reader learns that the boys were planning a mountain climbing trip to Katahdin. The final word prompts Henry to endure the journey alone to honor his brother's memory. In the end, he needs the help of three other climbers in order to do the difficult feat safely, so he is joined by Sanborn Brigham, his best friend. Then he meets Chay Chouan, a Cambodian ex-pat living in Maine (the person who hit Franklin with his car and killed him, but at first, Henry doesn't know this). Finally, Henry is joined by another person in need of healing, his sister Louisa.
As Henry climbs, he learns from his companions. Sanborn helps Henry to understand the ways that wealth and privilege have shaped his life. Chay makes him practice forgiveness, learning that although circumstances might pit us against one another, we are in this together after all. Finally, he learns that Louisa has been suffering in various serious ways throughout their life, meaning that suffering cannot be avoided. He also learns some unfortunate truths about his brother Franklin whose spoiled background had corrupted his character in painful ways.
By reaching the summit of the mountain, Henry learns that instead of his father's strategy of avoiding discomfort, pain, and sadness, Henry should build his house right in the center of tragedy, which he and his father call, "Trouble."
