Paris, 1896. Judith Fenwick and Coralie Vardon have survived their first encounter with the Midnight Exchange, but becoming lovers is easier than learning how to become partners.

When Judith is asked to examine conflicting records for a new Russian railway-securities issue, duplicate certificate numbers point toward a fraud large enough to ruin investors across Europe. A sealed diplomatic dispatch case is supposed to carry the evidence east on the new Nord Express. It is watched at every stage of the journey. At the German-Russian frontier, where passengers and luggage must transfer between incompatible railway gauges, the case appears never to leave official sight.

Yet when it is opened, the vital documents are gone.

The impossible theft draws Judith and Coralie from Paris through Brussels, Cologne, Berlin, Königsberg and the Russian frontier to St Petersburg. Judith follows contradictions in language, serial numbers and telegram chronology. Coralie follows the people who lie for money—and the ones who lie because they are afraid. Their pursuit exposes a market in forged securities and brings Coralie face to face with Madeleine Jarry, a former lover who knows exactly how quickly Coralie disappears when attachment begins to feel like confinement.

As the Midnight Exchange closes around them, the greatest danger may be the habit Coralie has never surrendered: making decisions for both women and calling it protection. To solve the case, Judith and Coralie must learn that trust is not the absence of secrets. It is knowing which truths belong to the person who shares the risk.

The Russian Sleeper is the second novel in The Adventuresses of the Midnight Train, an elegant Victorian railway adventure combining international intrigue, fair-play mystery, sophisticated heroines, and an adult sapphic romance.