Bideford, Devon, April 1873: the River Torridge is in flood. Almost as soon as she sets foot in the town, Abigail March saves a young woman from drowning.
Abigail, the daughter of a progressive Canadian politician, is in Bideford on official business, deputizing for her father. Accompanied by Inspector Theo Newton of Scotland Yard, she has travelled to the West Country to inspect the cache of smuggled weapons being guarded by the local borough police. That night, the woman Abigail saved is murdered and the weapons disappear. The police make an arrest, but when Abigail befriends Norman, the twelve-year-old brother of the accused man, she and Newton both realize that the police have made a mistake which could have tragic consequences.
At first, Newton is bewildered by Abigail. He has little experience of women and her forthrightness and ideas about women’s rights unsettle him. But, as their relationship progresses, Newton is inspired by her example. Spurred on by Abigail’s fearless determination and her sympathy for those less fortunate than herself, Newton shows bravery and strength, as they works tirelessly together to solve the case and uncover the truth.