Despite a new influx of well-heeled students, Michaelhouse has suffered from an acute lack of funds that has made itself manifest in a lack of decent provisions. It is only when the Brother in charge of the account books dies unexpectedly that an explanation is revealed: large amounts of money had been paid for goods the college never received. Although shocked by this evidence of fraud, Matthew Bartholomew is more concerned with the disappearance of a quantity of pennyroyal from his herbarium. Pennyroyal is known to cause a woman to miscarry, and a pregnant visitor to his sister's household has died from an overdose of the substance. Had she meant to abort her child, or had someone else wanted to ensure that she was unable to provide an heir to her husband's wealthy estates? When Matthew learns that it was the dead woman’s husband who had received Michaelhouse's missing money, he begins to search for other connections and quickly exposes a deep and treacherous conspiracy.