Lily's Crossing by Patricia Reilly Giff

"What will Gram say?" Lily asked. "She won't like it. She'll hate it. I know she will."

Poppy moved his hand, held it over Lily's wrist on the oar. "Gram knows."

Lily stared at him. "You told Gram first. You knew about it. Both of you keeping a secret . . . not telling me . . ."

She shook his hand off her wrist, feeling tears hot in her eyes, a terrible burning in her throat, feeling angry enough to burst. She hated him, hated Gram. (34)

Lily's summer is starting off very badly, even though she's staying in Rockaway by the Atlantic Ocean with her grandmother just like she always does. However, her best friend Margaret is moving with her family to Detroit, and her father is called overseas to serve as an engineer in World War II. Finally, she's strapped with the neighbor's nephew from overseas, who Lily is suspicious about. While teaching him to swim and rescuing an abandoned cat bring them together, one of Lily's infamous lies might just tear this budding friendship apart. As a companion novel to Willow Run, Patricia Reilly Giff presents Lily's side of the story in Lily's Crossing.
AMY