The Mapledurham Watermill, situated on the River Thames in Oxfordshire, is used as a background in a few scenes and as the subject of one of Hazel's paintings. This mill was also notably used on the cover of Black Sabbath's 1970 self-titled debut album.
The original story can be found in 'The 13 Problems', a collection of short stories told at Miss Marple's home by her companions and solved by Miss Marple on the spot.
When Eddie says he is going 'to force the moment to its crisis' he is quoting the poem 'The Love Song of J. Alfred Prufrock' by T.S. Eliot.
Last UK TV role of Donald Sinden.
The original Marple short stories had various narrator characters presenting mystery stories, and Jane Marple deducing their solutions from certain details. In "The Blue Geranium", the narrator was Arthur Bantry, a friend of George Pritchard.