Mount Katahdin is a real mountainl located in Baxter State Park, Piscataquis County, Maine. It is the tallest mountain in the state.
The main character in Trouble, Henry, once had a climbing accident that he was lucky to escape from uninjured and his older brother, Franklin, promised him that he would teach him how to climb properly. One day, if he was good enough, they could climb Mount Katahdin, together.
Franklin finally agrees to take Henry to Katahdin for Henry's fourteenth birthday. Unfortunately, on the day before they leave, Franklin is run over by a car while he is out jogging. Moments before dies he mutters the word Katahdin. Henry takes that as a sign that he must climb the mountain on his own.