Katherine Schneider’s life as a dentist in 1913 New York is upended when a patient reveals details of a deadly plot while under the influence of laughing gas. As she is plunged into danger, she seeks help from the dashing Lieutenant Jonathan Birch, a police officer she has long admired from afar.

Patrick O'Neill survived a hardscrabble youth to become a lawyer for the downtrodden Irish immigrants in his community. He's proud of his work, even though he struggles to afford his ramshackle law office. All that changes when he accepts a case that is sure to emphasize the Blackstones' legacy of greed and corruption by resurrecting a 30-year-old mystery. Little does Patrick suspect that the Blackstones will launch their most sympathetic family member to derail him. 

When the backlash from her work forces a return home to Baltimore, Clara finds herself face to face with a childhood sweetheart who is no longer the impoverished factory worker she once knew. In her absence, Daniel Tremain has become a powerful industry giant and Clara finds him as enigmatic as ever. However, Daniel's success is fueled by resentment from past wounds and Clara's deeply held beliefs about God's grace force Daniel to confront his own motives.

Anna O'Brien leads a predictable and quiet life as a map librarian at the illustrious Library of Congress until she stumbles across the baffling mystery of a ship disappeared at sea. Thwarted in her attempts to uncover information, her determination outweighs her shyness and she turns to a dashing congressman for help. Luke Callahan was one of the nation's most powerful congressmen before his promising career was shadowed in scandal. Eager to share in a new cause and intrigued by the winsome librarian, he joins forces with Anna to solve the mystery of the lost ship. 

When their father's death leaves them impoverished, Sarah Summers and her genteel sisters fear they will be forced to sell the house and separate to earn livelihoods as governesses or companions. Determined to stay together, Sarah convinces them to open their seaside home to guests to make ends meet and provide for their ailing mother. Instead of the elderly invalids they expect to receive, however, they find themselves hosting eligible gentlemen. Sarah is soon torn between a growing attraction to a mysterious Scottish widower and duty to her family.