The novel upon which this episode is based is the first story Agatha Christie would write based in the town she was born: Torquay, Devon, England.
The first two-parter in the series.
Pauline Moran (Miss Lemon), who appears in the second half, does not receive her normal onscreen credit in the opening titles. Similarly, Elizabeth Downes (Maggie Buckley), who is only in the first half, does not appear in the closing credits. This is a result of the two previously separate parts being joined together and, therefore, has the opening titles of part 1 and the closing credits from part 2.
The song Freddie and Jim are dancing to at the beginning, 'Love is the Sweetest Thing', is the same one Jackie and Simon dance to at the end of Death on the Nile (2004)
At the dinner at End House before the fireworks, all the guests are wearing black, white, red, or a combination of those three colors. Similarly, at the gathering of all the characters near the end of the movie, everyone is wearing black, white, or shades of gray (except for Mr. and Mrs. Croft, the two servants, and Inspector Japp, which emphasizes that they are not among the upper class).