Dorothy L. Sayers
— $6.99 — Book
This novel deals with a mystery unlike any that Lord Peter Wimsey has ever dealt with before; there's a suspect with motive and means to have killed the man in question, who has recently written a novel very similar to the circumstances of the murder, and who cannot offer a believable defense - yet Lord Peter believes she is innocent, and has to prove that the death - by arsenic poisoning - was either a suicide or caused by somebody else.
To make matters more interesting, the woman he wishes to save, Harriet Vane, is someone he fell for the moment he saw her. (She is not so calm about the situation, at first dismissing him entirely, and later putting him off.) And her (second) trial is coming up swiftly; Peter only has a few weeks to determine a motive and discover the means, or Harriet will be convicted and hanged.
This is one of the classics of the mystery genre; the reader is given most of the pieces at the start of the novel, yet has to rely on Lord Peter to unravel the innocence of Harriet Vane.