Could one rare plant hold the key to a thousand riches?

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 past in London behind her. As she settles into her new home, she becomes interested in the Botanic Garden which borders the house and offers her services as an artist to record the rare plant's impending bloom. In this pursuit, she meets Belle Brodie, a young woman with a passion for botany and the art of perfume creation.

Belle is determined to keep both her real identity and the reason for her interest in 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... And when they are revealed, they can carry the greatest of consequences...