Lily's Crossing by Patricia Reilly Giff is the story of Lily Mollahan and what happens when she tells one lie too many.

Lily lives in St. Albans, Queens, with her father and her grandmother. Lily's mother died when Lily was a very small girl, but Lily is content to be who and where she is. Every summer, Lily, Poppy (her father) and Gram live in Gram's house on stilts in Rockaway, near the Atlantic ocean. To Lily, Rockaway is a world apart from the routine of St. Albans with its endless school days and interminable winters. At the beach, Lily can really relax and explore the world. She and her friend Margaret Dillon spend their time gossiping and going to the movies. But there are things that bother Lily about her ten-year-old life. The first thing is the matter of friends. Without Margaret, Lily would be completely without a confidante. Next on Lily's list of problems is lying. Lily does not mind telling lies on a regular basis. It is more exciting for Lily that Margaret believes Poppy is in the Secret Service or that Aunt Celia is a spy living all the way over in Berlin.

This particular summer, though, there is something different happening in the world. It is 1944 when the narrative begins, and World War II is being fought in Europe. Margaret's family is moving to Detroit, where her father will assemble airplanes. Eddie Dillon, Margaret's older brother and a soldier, goes missing on one of the most important days of the war and the small community begins to feel afraid. Meanwhile, Lily must accept the idea that she needs to find a friend to replace Margaret. With no possible friends on the horizon, Lily decides to follow Albert Orban. Albert is a recent refugee from Hungary who has no interest in being friends with Lily Mollahan at all, much to Lily's surprise. When a kitten is thrown into the ocean and left to drown, Lily and Albert join forces and later become wary friends.

When Poppy goes overseas, everything changes for Lily and Gram. Not knowing where Poppy is or when he will return gives Lily a new perspective on the war. Lily also comes to appreciate Albert's overwhelming desire to learn to swim. When Albert talks about his life in Hungary, Lily can hear the wistfulness in his voice. Albert will do anything he can to find his sister Ruth again, even if it means endangering his own life.

During the summer before going into sixth grade, Lily Mollahan loses her best summer friend, saves a life, cracks a code, and learns something truly valuable about truth, family, and war.