In "The Red Convertible," Susy and the brothers' adventure with her represents a last carefree episode for Henry before he goes off to war. After the war, he is forever changed. Before the war, however, Henry and his brother, Lyman buy a car, a red convertible. They spend the summer driving around, making memories that the narrator falls back on when Henry returns traumatized by the war.
Susy forms a key part of those memories. Lyman tells us that "We went places in that car, me and Henry. We took off driving all one whole summer." One day, they pick up Susy, a hitchhiker, who is heading to Alaska. Once they arrive in Alaska, they "never wanted to leave." Their lifestyle in Alaska is simple, and they feel connected to nature. The boys stay with Susy's family, who "fed us and put us up." Lyman remembers the brothers having fun conversations with Susy. Again, this is a carefree time for Henry and his half-brother, Lyman. This is an innocent precursor to the experiences that will soon change Henry forever.
Later in the story, Henry returns home from war and is obviously traumatized by what he has seen and done. He eventually commits suicide by jumping in the river and drowning. Lyman drives the convertible into the river, where it remains forever exclusively connected to Henry. This car that once drove them around the country symbolized their innocence and carefree youth, as did Susy. Once Henry goes to war and returns, this innocence is lost.