Invincible Summer introduces illness and death into what might otherwise be a standard teen love story. Here, first love is also a last look at life, and the rites of passage into romance, sexuality, and intimacy are intensified and thrust into profound paradox by approaching death. Robin and Rick meet in the hospital where she has come for a battery of tests, and he for chemotherapy. Both have acute lymphocytic leukemia. He’s been sick for two years. She’s just finding out about her own condition.

Robin lives with her father, who can hardly bear to be around her illness, and her grandmother, who, since her mother died years ago in a car accident, is the primary caretaker. The father’s love has to be understood and accepted in light of his emotional limitations. The book thoughtfully explores how sickness rearranges family systems as well as treating familiar young adult themes of separation from friends, wanting sex, embarrassment about physical appearance, uncertainty of remission, and how to talk about the future.

After Rick’s death, at which Robin is present, Robin recalls a game her mother used to play, called "The Worst Thing." "What’s there to be afraid of? What’s the worst thing that could happen?" The aim of the game is to look at the worst case until it seems manageable, because for every worst thing, there is some way through to remedy or acceptance. The game, reproduced as internal dialogue, drives to ultimate questions, ending with something like Pascal’s wager--a version of intellectual comfort that will do in the absence of positive faith in the promise of afterlife.