- Actor-Shared Background: Much like Lady Eddison, Felicity Kendal in her real life also spent some time in India where she's been brought up as a result of which she now speaks Hindi as well.
- Deleted Role: Daphne Oxenford filmed scenes as Agatha Christie on her deathbed in 1976 but these were removed during editing. It overlaps with Deleted Scene, viewable on the Series 4 DVD releases with commentary from Russell T. Davies.
- Hey, It's That Place!: This episode was filmed at Athelhampton House, a beautiful Manor House in Dorset England. "Seeds of Doom" also used this location and the movies Sleuth and From Time To Time were shot here as well.
- Real-Life Relative: David Tennant's father Sandy MacDonald makes a cameo as a footman. He was visiting David on set and was offered a part on the spot - and he confessed he was glad he didn't have to learn lines.
- Wag the Director: Originally, The Doctor was to have rammed the Vespiform into the lake with the car that he and Donna had commandeered. David Tennant objected because he was concerned that that ending would portray the Doctor as a murderer.
- What Could Have Been:
Donna: It's like Ten Little -The Doctor: Niggles aside, we'd better look in the library.
- Initially, Russell T. Davies and Gareth Roberts envisioned setting the story in the mid-Sixties, depicting an elderly Agatha Christie who could be portrayed in the manner of Miss Marple. However, they soon came to realise that a relatively modern setting would not convey the desired flavour of a classic Christie novel. And as listed under Deleted Role, they also filmed scenes for a planned framing device wherein the events of the episode were book-ended around the Doctor and Donna visiting Agatha on her deathbed.
- The role of Lady Eddison was offered to Helen Mirren.
- The script originally contained a reference to Ten Little Niggers, which was dropped for being too risky:
- You Look Familiar: Christopher Benjamin (The Colonel) previously played Henry Gordon Jago.
Trivia / Doctor Who S30 E7 "The Unicorn and the Wasp"