Roddy Winter is about to marry Elinor Carlisle, but what is his relationship with his old flame, Mary Gerrard? Then Mary dies suddenly - she was poisoned. All the evidence points overwhelmingly to Elinor being the killer, but she insists she has been framed.
Poirot is called in to look into the killing on Elinor's behalf, and he quickly decides there is more to the case than meets the eye.