Billy is nine when he finds out, accidentally, that he's adopted. Feeling betrayed, he retreats into a world of his own, cuts his mother and father off completely and builds up his own Fortress of Solitude, modeling his life after that of the most famous orphan ever, Superman. His only ally, friend and sometimes enemy, is Kim, who watches Billy as they both grow through high school, and who is frustrated by Billy's determination not to need anyone but himself. When Billy is forced finally to admit this need, it is a shattering moment, but with Kim's help, the pieces of his life can be rearranged, put back together to build something new and stronger, based on mutual need and friendship.