Based upon a historical event-a network of undercover volunteers plot to prevent Japanese saboteurs from invading the Columbia River during World War II. Oklahoma Dust Bowl survivor Anne Mettles creates a floating library to provide books and materials for Columbia River residents. But wartime budgets slash funding, and Washington's governor can only find money if Anne will conduct secret military surveillance along the river to monitor and report any enemy activity. Anne wants to operate Books Afloat alone but must accept help to pilot the boat. Mechanic Ted Vincent insists on being onboard and discovers that unusual boat damages are not accidents, but sabotage. A young man who will do anything to win Anne's affections and an ambitious reporter writing public interest stories also ride along, complicating matters. Anne and team hazard their lives to save the nation they love and discover newfound courage, giving her and Ted a chance at love-if they can survive.