In 1899, a secret society tried to use a young woman to bring an ancient evil into the world. Twenty years later they will return to finish the job. After the Great War, London is settling once more into the gentle routine of peacetime. The airships that once protected England's coast now ferry people back and forth across the Thames, the magically-inclined are free to return to their normal work, and those who seek treasures left behind by ancient civilizations are again free to explore. Dorothy Boone shunned a life of luxury to follow in her grandmother's footsteps by uncovering the mysteries of "the worlds that came before ours." When a package explodes upon delivery to Lady Boone's townhouse, she is drawn into an unlikely alliance with her nemesis, Trafalgar of Abyssinia, to find the culprit. They soon find themselves unraveling a plot that has left many of their allies dead and the rest in fear for their lives. A group of treasure hunters with a fiendish plot to take over England has begun eliminating its competition in order to fund an expedition to retrieve the last item they need for a summoning that will bring an ancient evil into our world. With no one else to trust, Trafalgar and Boone must put aside their differences and forge a partnership to stop their mutual enemy. If they fail, a world that still bears the scars of the Great War will be once again thrown into turmoil. Welcome to the world of Trafalgar and Boone, a world where airships battled in a Great War that was fought by soldiers who utilized magic and summoned monsters to do their bidding, a world that they must defend by working together to stop an evil far greater than either of them could ever have imagined.

Dorothy Boone's attempt to help a friend leads her to an encounter with a deadly new rival. Trafalgar and Boone have been working together for a year, taking small commissions in order to learn how to work together. When a friend and colleague is committed to an asylum following a disastrous mission in the Mediterranean, Dorothy takes it upon herself to uncover the truth. What she finds is that her friend was close to the discovery of a lifetime: the remnants of a prehistoric civilization who might have been wiped out by the Biblical Flood. Trafalgar agrees to accompany her on an expedition to finish what her friend began, and soon they run afoul of a powerful enemy: Emmeline Potter, called Virago, is a treasure hunter who is also adept at magic and seeks riches to help fund a violent uprising. Dorothy and Trafalgar must race to defeat their unscrupulous opponent if they hope to preserve the site for future generations, but they soon discover Virago may be the least of their worries. The secrets of the past have ways of remaining hidden, and trying to uncover them may cost Dorothy her life.

Miss Trafalgar and Dorothy Boone have grown comfortable in their partnership. The rough edges on the society they formed with their fellow adventurers have begun to smoothe, opening the doors for a new era of cooperation among one-time enemies. When Trafalgar receives an Egyptian statue, a gift from her former assistant, she asks Dorothy to determine its authenticity. What Dorothy uncovers throws both of them, along with the rest of the Mnemosyne Society, into chaos. With lives at risk and the future at stake, Trafalgar leads a group of reluctant allies from London to Egypt to stop an unspeakable power from falling into the wrong hands. Meanwhile, Beatrice Sek continues her quest to discover her true origins. Armed only with the knowledge that she is one of four "Elementals," she spends her spare time searching for anyone who may know where she came from. She receives unexpected assistance from a former foe, a powerful enemy who promises to help her find answers. The offer is too good to refuse, no matter who it's coming from, but Beatrice may soon find herself forced to choose between revelation and surrendering her soul.

Dorothy Boone, still blaming herself for a devastating loss on their last adventure, and Miss Trafalgar are offered a new mission from the Royal Geographical Society: an expedition to find the source of a mythical river has gone missing in the Amazon rainforest, and their patrons want them found. It seems like the perfect low-threat endeavor to get the duo back to normalcy, so Dorothy and Trafalgar accept. Accompanied by Cora Hyde, who is also recovering from a loss, the duo sets out for the jungle. Their safe undertaking soon turns perilous when they run afoul of a previously unknown tribe known as the Burnt Empire. Dorothy and Trafalgar are separated in the scuffle and taken in by two groups with similar goals but differing tactics. The groups only agree on one point: the very existence of the Burnt Empire could lead to untold destruction.