It's the summer of 1822 and Edinburgh is abuzz with rumours of King George IV's impending visit. In botanical circles, however, a different kind of excitement has gripped the city. In the newly-installed Botanic Garden, the Agave Americana plant looks set to flower, an event that only occurs once every few decades. When newly widowed Elizabeth arrives in Edinburgh to live with her late husband's aunt Clementina, she's determined to put her unhappy past in London behind her. As she settles into her new home, she becomes fascinated by the beautiful Botanic Garden which borders the grand house and offers her services as an artist to record the rare plant's impending bloom. In this pursuit, she meets Belle Brodie, a vivacious young woman with a passion for botany and the lucrative, dark art of perfume creation. Belle is determined to keep both her real identity and the reason for her interest the Garden secret from her new friend. But as Elizabeth and Belle are about to discover, secrets don't last long in this Enlightenment city.