what is the subplot or subplots in this book a separate peace?
The first subplot that comes to mind would be Leper's experience with the war. Chapter 10 focuses on Leper after he is discharged from the military because of a psychological breakdown that he has at basic training. Before that time, Leper was briefly mentioned as a bystander who observed and witnessed Gene's and Finny's adventures. Gene speaks to him once as he is cross-country skiing and learns a little bit more about him before he signs up to be on a skiing group in the military. The main story, of course is about Gene and Finny, but the story about Leper brings out another interesting perspective of the time at Devon and the boys who faced World War II in the 1940s. Other subplots to consider might be Gene's life without Finny, Brinker, and training for the Olympics of 1944.