Jessamine Luxson lives with her father, Thomas, an apothecary, in an isolated cottage near Alnwick Castle. Thomas's pride and obsession is his locked garden full of dangerous plants, which Jessamine is forbidden to enter.
When a traveler brings an orphan to their cottage, he claims the boy has special gifts that Thomas might value. Jessamine is drawn to the strange but intriguing boy, called Weed. Soon their friendship deepens into love. Finally, Weed shares his secret: he can communicate with plants. For him they have distinct personalities-and some are even murderous. From the locked garden the poisonous plants call to Weed, luring him with promises of deadly power.
When Jessamine falls inexplicably ill, only Weed's relationship with the Poisons can save her. But Thomas is determined to exploit Weed's abilities, even if it risks Jessamine's life-or drives Weed to the brink of madness...