Eustacia Rose's life is beginning to return to normal: she is back teaching at UCL and her relationship with Matilde is blossoming. But when a man is found dead with a needle in his neck, that fragile peace begins to crumble. Eustacia finds a painting of herself with a syringe next to her neck and discovers that there are other people who seem to know more about the killing than they are letting on.

The threat around Eustacia only increases as a PhD student begins to stalk and harass her to gain access to her poisonous plant collection. After Eustacia continually refuses, he contacts a lab that is illegally selling synthetic plant toxins but turns up dead shortly after. As the body count rises, Eustacia has no choice but to investigate the deaths in earnest.