The Counterfeit Lady

Victorian mysteries from the USA Today bestselling author of the Deadly Series.
Enter the London of hansom cabs and gas lights to combat crime and bring killers to justice.
Georgia Fenchurch is a demure Victorian spinster and part of the secretive investigative group the Archivist Society. She is both a quiet antiquarian bookseller and adventurous hunter of killers and thieves.
The enigmatic Duke of Blackford returns to Georgia's life asking for her help and that of the Archivist Society in retrieving stolen blueprints. The plans are for an advanced battleship that will preserve Britain's mastery of the seas. Spies from various countries are descending on London in the hunt for the blueprints, ready to enter into a bidding war.
Blackford wants Georgia to play an old love of his, newly widowed and returned from the colonies to move among high society. He sends her out to search in Mayfair's glittering ballrooms and opulent drawing rooms. As they try to learn which spy has killed to gain the plans that will destroy Britain's dominance on the oceans, Georgia receives messages saying her secret is known and she won't live to find the killer.
These are clean reads, with no scary, on-stage violence, swearing, or sex.