A mystery author Harriet Vane is on trial for the murder of her former lover, Phillip Boyes, a colleague writer with strong views on atheism, anarchy, and free love. Harriet is accused that she has poisoned him with poisons she had bought under false names, but she claims that she was only buying them as a research for her new novel which involves dealing with poisons. As the trial results in a hung jury and the judge orders a re-trial. Lord Peter Wimsey visits Harriet in prison, declares his conviction of her innocence and promises to catch the real murderer.