Three years into the Great War, England's greatest asset is their intelligence network - field agents risking their lives to gather information, and codebreakers able to crack every German telegram. Margot De Wilde thrives in the environment of the secretive Room 40, where she spends her days deciphering intercepted messages. But when her world is turned upside down by an unexpected loss, for the first time in her life numbers aren't enough.

Left with an estate on the brink of bankruptcy after their father's death, Lady Marigold Fairfax and her brother open a private investigation firm marketed to the elite . . . to spy on the elite. Dubbed The Imposters, Ltd., their anonymous group soon becomes the go-to for the crème of society when they want answers delivered surreptitiously. But the many secrets Marigold learns about her peers pale in comparison to her shock when she and her brother are hired to investigate her best friend's father as a potential traitor.

When Miss Charlotte Wilson asks God for a husband, she decides He must want her to pursue Mr. Hamilton Beckett, the catch of the season. The only problem? She's never actually met Hamilton. Fortunately, one of her oldest and dearest friends, Mr. Henry St. James - who has returned to New York after a two-year absence - does know Hamilton. Much to Henry's chagrin, Charlotte immediately ropes him into helping her meet Hamilton. However, none of her plans to catch Hamilton's eye go as she expected, and she is even more confused when her old feelings for Henry begin to resurrect themselves.

1906: Lady Elizabeth “Libby” Sinclair, with her love of microscopes and nature, isn’t favored in society. She flees to the beautiful Isles of Scilly for the summer and stumbles onto the dangerous secrets left behind by her holiday cottage’s former occupant, also named Elizabeth, who mysteriously vanished. Oliver Tremayne - gentleman and clergyman - is determined to discover what happened to his sister, with the help of the girl now living in what should have been Beth’s summer cottage...especially when he realizes it’s the curious young lady he met briefly two years ago.

Forced to run for her life, Kit FitzGilbert finds herself in the very place she swore never to return to - a London ballroom. There she encounters Graham, Lord Wharton, who believes Kit holds the key to a mystery he's trying to solve. As much as she wishes that she could tell him everything, she can't reveal the truth without endangering those she loves.