Susanna, Lady Appleton, has been wearing widow's weeds for the past year and a half. But when a coded letter from her late husband, Robert, instructs her to meet him at a London alehouse, Susanna knows that his "death" was merely a ruse. Strangely, Robert doesn't show up, but is later found tumbling down the steps of the Eleanor Cross in a crowded town square.

Though many in the crowd assume he's fallen in a drunken stupor, Susanna, an expert herbalist, is shocked to find that Robert's skin tone and clenched fists show the telltale signs of poisoning. But Lady Appleton's knowledge about poisons backfires as she herself is accused of the crime and arrested. She will burn at the stake - unless she can track down the true killer.