A London apothecary quietly sells poison to women to seek
revenge on the men who have wronged them. The potion must never be used against
other women, and the murderer and victim must be recorded in the apothecary’s
register. In 1791, a child tries to acquire a dose, setting in motion a chain
of events that threatens to expose the whole operation. Meanwhile, in present day,
a vial washes ashore the Thames and is discovered by Caroline, who sets out to
uncover unsolved crimes.