London, 1923. Returning from Paris, botanical researcher Saffron Everleigh finds that her former love interest Alexander Ashton's brother, Adrian, is being investigated for murder. A Russian scientist working for the English government has been poisoned, and expired in Adrian's train compartment. Alexander asks Saffron to put in a good word for Adrian with Inspector Green. Despite her unresolved feelings for Alexander, Saffron begins to unravel mysteries surrounding the dead scientist. As if a murder case weren't enough, her best friend Elizabeth's war-hero brother, Nick, arrives in town and takes an immediate interest in Saffron. Saffron learns Alexander has been keeping secrets from her, including a connection to Nick, who Saffron and Elizabeth begin to suspect is more than he seems. When another scientist is found dead, Saffron agrees to go undercover at the government laboratory. Risking her career and her safety, she learns there are many more interested parties and dangerous secrets to uncover than she'd realized. But some secrets, Saffron will find, are better left undiscovered.