Agatha Christie's Marple - Season 3 Episode 4 -

Jason Rafiel, an old friend of Miss Marple's, dies and leaves her an unusual legacy, to grant his final wish: she has to uncover a possible murder that may or may not have happened already. All she gets are two tickets to a Mystery Bus Tour and the advice to invite someone trustworthy to the bus trip, the only thing she knows about the crime being the single word 'nemesis'.