- Acting in the Dark: The actors were not told who the actual murderer is.
- Actor Allusion:
- Name's the Same: Chloe's boyfriend Dean Thomas. Alfred Enoch, who plays Dean in the movies, shows up at one point as well, to add to the confusion.
- Playing Against Type: David Bradley makes a rare appearance as an extremely sympathetic character, albeit one set up to look like a creep.
- Throw It In: "I just want you to know, I think you're a truly horrible person." Ironically one of the very few things about Series 2 that just about everyone loves.
- Doctor Who cast reunited:
- David Tennant (Tenth Doctor), Olivia Colman (Prisoner Zero from "The Eleventh Hour"), Arthur Darvill (Rory Williams), Jonathan Bailey (Psi from "Time Heist"), Eve Myles (Gwyneth from "The Unquiet Dead" and Gwen Cooper from Torchwood), Meera Syal (Dr Nasreen Chaudhry from "The Hungry Earth"/"Cold Blood"), Adjoa Andoh (Francine Jones), Peter De Jersey (Androgar from "The Day of the Doctor") and David Bradley, who played William Hartnell in An Adventure in Space and Time (plus the villain in "Dinosaurs on a Spaceship" and the First Doctor in "Twice Upon A Time"), all appear here.
- A few Torchwood cast members are also reunited: As well as Eve Myles, Susan Brown (Bridget Spears), Lucy Gohu (Alice Carter), and Matthew Graville (Doctor from "End of Days") appear.
- Jodie Whittaker, one of the few cast members who hadn't been on Doctor Who, retroactively became an example after being announced as the Thirteenth Doctor.
- During production of Season 1, nearly everyone - including David Tennant himself - was Locked Out of the Loop concerning the killer's true identity to prevent potential leaks. Olivia Colman was one of the few people told early on, with most not finding out until The Reveal was looming.