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 stabbed with a syringe 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.