The United States is at war with Germany. Fourteen-year-old Jill Winter's mother is traveling to Newfoundland to be with Jill's sick uncle and must pass through the treacherous North Atlantic where German submarines -- U-boats -- stalk like wolves. Jill's father, a famous pop singer, is on tour, so Jill is sent to Winter Haven, Maine, to stay with Nana.

Quarry, a local boy, says that "gossip ain't never been so good," and Jill soon discovers he's right -- Winter Haven is full of secrets and rumors. First there's Wendy, a teenager who's visiting her aunt Adrie, the owner of a local inn, and who tells so many fanciful stories and secrets, it's hard to know what's true. Then there are the Crystals, a snobbish girls' club, who blackball Wendy because of a dark secret they reveal to Jill. Even Nana seems to be keeping secrets -- with her Germanfriend Ida Wilmar! Who's a friend and who's an enemy?

As German subs torpedo American and Canadian ships off the Maine coast, Jill is anxious for her mother's safety. Her fears are heightened when she finds a wounded pigeon with the message Sonnabend ivattached to its leg! When Nana and Ida Wilmar whisper to each other and Jill hears that same word -- Sonnabend -- she determines to uncover the truth behind the mysteries in Winter Haven. But she soon finds herself in grave danger when she uncovers the biggest secret of all -- and must run for her life!

Based on startling historical events that took place in the harbors of Maine during World War II, Shadows on the Seais a fast-paced mystery that will keep readers guessing from beginning to end.