Miss Marple believes she's seen a murder in a passing-by train, yet when the police find no evidence she decides to investigate it on her own.
The unassuming, nebbishy inventor Sidney Stratton creates a miraculous fabric that will never be dirty or worn out. Clearly he can make a fortune selling clothes made of the material, but may cause a crisis in the process. After all, once someone buys one of his suits they won't ever have to fix them or buy another one, and the clothing industry will collapse overnight. Nevertheless, Sidney is determined to put his invention on the market, forcing the clothing factory bigwigs to resort to more desperate measures...
A murderer is brought to court and only Miss Marple is unconvinced of his innocence. Once again she begins her own investigation.
