Who Frank Parris is
Frank Parris is the difficult guest murdered at Branlow Hall on Cecily and Aiden’s wedding day. Years later, his death remains the event around which the hotel’s memories are organised. Stefan Leonida’s conviction appears to have closed the case until Cecily reads Alan Conway’s novel and believes it points to another answer.
Role in Moonflower Murders
Frank’s behaviour at the hotel matters as much as his identity. Complaints, a supposedly faulty keycard and an announced trip to the opera look like the habits of an unpleasant guest. Susan gradually asks whether they were messages directed at a particular person. The investigation turns apparently incidental conversation into evidence about what Frank knew and how he intended to use it.
Key relationships
Aiden MacNeil encounters him before the wedding. James Taylor knows him from an earlier part of his life and explains his connection with Alan. Susan Ryeland reconstructs that history. His fictional counterpart is Oscar Berlin.
Played by Mark Gatiss
Mark Gatiss plays Frank Parris. Gatiss’s paired roles allow the adaptation to compare a contemporary hotel guest with a period film producer. Recognising that casting link should prompt questions about Conway’s choices, not an assumption that their biographies match.
Their story and fate — spoilers
Frank recognised Aiden as Leo, a former escort, and used the information to demand sex. His keycard and opera remarks were part of the coercion. Aiden killed him and framed Stefan. Frank’s cruelty therefore explains the immediate pressure behind the crime without excusing the murder or the calculated destruction of an innocent man’s life.
Books and television — book spoilers
Mark Gatiss also plays film producer Oscar Berlin in Conway’s novel. The same face joins two men whose social standing gives them access to other people’s vulnerabilities. The resemblance is only one layer of the book’s clues: its dedication to Frank and Leo, and the lion references Susan initially treats as decorative, are more directly connected with Frank’s concealed relationship to Aiden.
Role in the story
Frank is introduced through the disruption he causes at a busy hotel. The family is preparing for a wedding, yet his complaints demand attention from Aiden and the staff. Because the story is reconstructed years later, an apparently ordinary grievance about a room can return with a different meaning once Susan knows more about the guest who made it.
His place in the mystery extends beyond Branlow Hall. James Taylor can explain a part of Frank's earlier life that the hotel family cannot, while the dispute over property gives Susan a separate reason to question his relatives. Keeping those connections distinct is helpful. A person may have made several people unhappy, but the existence of several grievances does not establish which one led to a killing.
Key scenes by episode
Follow the linked episodes as you watch. Open the scene notes when you want more detail.
Episode scenes (full spoilers)
Episode 1: Frank’s arrival, complaints and move to the Moonflower wing place him in the wedding party’s memory before the discovery of his body. The original investigation leads to Stefan’s conviction, leaving the guest’s own intentions less fully understood.
Episode 3: Sajid explains that Frank wanted to sell the house jointly owned with Joanne after his business failed. The Websters could not afford to buy him out. Susan finds a substantial financial grievance, but still needs a connection to the hotel crime.
Episode 4: James tells Susan that Frank introduced him to Alan. The recollection of another escort called Leo opens a line of inquiry outside the Treherne family. The keycard and opera remarks also return in the wedding flashback and Conway’s interviews.
Episode 6: The remarks are explained as coercion directed at Aiden, whom Frank recognised as Leo. Aiden’s response was murder and the deliberate framing of Stefan. Frank’s behaviour helps explain the immediate pressure without excusing either crime.
In the book
Book and screen comparison (book spoilers)
Oscar Berlin is the fictional counterpart played by Mark Gatiss. Conway changes a hotel guest into a film producer, so the shared face should not be taken as a shared biography. For the completed puzzle, the dedication to Frank and Leo is a more direct connection to the real-world events than the casting resemblance. Keep the dedication in mind when returning to Susan's conversations with James. Conway has used people he knows both as models for characters and as the basis of a word game, giving his editor two different ways to approach the same history.
What to notice on a rewatch (spoilers)
For the clearest sequence, revisit the wedding flashback before reading Susan's final explanation. Watch who receives the keycard and who notices the problem with the opera story. Those are small conversational details at first, but the finale gives each a particular purpose.
Sources (checked 19 October 2026): PBS: Moonflower Murders cast and characters, PBS: Moonflower Murders, episode 1, PBS: Moonflower Murders, episode 4, PBS: Moonflower Murders, episode 6
Read or listen to the book
Moonflower Murders (2020)
Anthony Horowitz’s novel behind the second television mystery.
Waterstones · print Audible · audiobookPaid links may earn commission, at no extra cost.
Mark Gatiss plays both Frank Parris and Oscar Berlin, connecting the two story worlds.