Who Aiden MacNeil is
Aiden MacNeil is Cecily’s husband and works on publicity for Branlow Hall, the hotel owned by her parents. When Cecily disappears, he appears to Susan as a frightened partner and a father caring for their daughter Roxana. His public role and private crisis are closely connected.
Role in Moonflower Murders
Aiden’s wedding to Cecily took place on the day hotel guest Frank Parris was murdered. Years later, Cecily’s reading of a Conway novel brings that earlier event back into the family’s life. Aiden must answer Susan’s questions about both occasions. His professional experience in presenting a convincing account is particularly interesting in a story where appearances and carefully chosen words can conceal as much as they reveal.
Key relationships
Lawrence Treherne and Pauline Treherne are his parents-in-law; Lisa Treherne is Cecily’s sister. Frank Parris connects his past to the wedding. His fictional mirror is Algernon Marsh, also played by Tudor.
Played by Will Tudor
Will Tudor plays Aiden MacNeil. Tudor also plays Algernon Marsh, Melissa’s financial manager. The two men share a polished appearance and compromised dealings, but their roles in the solutions are different.
Their story and fate — spoilers
Susan identifies Aiden as the former escort known as Leo. Frank recognised him and used that knowledge to demand sex before the wedding. Aiden murdered Frank and framed Stefan Leonida, exploiting Stefan’s clothing, toolbox and vulnerability. When Cecily recognised the meaning of Conway’s clues, Aiden killed her too. Susan exposes him at the final gathering, and the police take him away.
Books and television — book spoilers
The television ending arrests Aiden, whereas the novel gives him a final letter and a fatal encounter with a train after his escape. Another connection survives the adaptation: Aiden MacNeil and Madeline Cain are anagrams. Susan explicitly recognises that wordplay in the novel; the screen leaves it as a last discovery for the viewer. Tudor’s dual casting with Algernon is therefore only one of the links that Conway has planted.
Role in the story
Aiden connects the two events Susan has been asked to understand. He was the bridegroom when Frank Parris died at Branlow Hall, and he is the husband left behind when Cecily disappears years later. His job in publicity adds a professional layer to the public appeals and family explanations: he is accustomed to presenting the hotel to other people.
The contrast between the wedding and the disappearance is an important part of his introduction. What should have been a family celebration has become the background to an old murder, while the present crisis interrupts the domestic life built afterwards. Susan needs an accurate account of both periods. Remembering Aiden's position in each helps keep the flashbacks clear without treating a distressed appearance as a complete explanation.
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: Aiden deals with Frank’s complaints and finds him a room in the Moonflower wing despite the pressure of the wedding bookings. This places the bridegroom and guest in direct contact before the murder.
Episode 3: Aiden makes a television appeal for Cecily with Locke alongside him. He also objects to the expense of Susan’s work, showing that the family’s decision to employ her has not removed the disagreement about her investigation.
Episode 4: Frank gives Aiden his supposedly faulty keycard and mentions The Marriage of Figaro. Cecily knows the opera is not being performed that evening. Later, Conway’s recordings preserve Aiden interrupting her interview.
Episode 6: Susan identifies Aiden as Leo and reconstructs the killing of Frank, the framing of Stefan and the murder of Cecily. The keycard, opera reference, missing fountain pen and staged sighting acquire a connected explanation. The police arrest him at the final gathering.
In the book
Book and screen comparison (book spoilers)
There is a clear difference in the ending: television ends Aiden's story with arrest, while the novel includes a final letter and a fatal encounter with a train after his escape. The Madeline Cain anagram also works differently for the audience. Susan explicitly recognises it in the novel; television leaves the final recognition to the viewer. Both points belong behind a book-spoiler warning because they concern the completed solution.
What to notice on a rewatch (spoilers)
Algernon Marsh is Aiden's visible counterpart, but the wordplay connects him elsewhere too. That distinction is a good reason to follow names as well as actors. The casting gives one route through Conway's inventions; the dedication and anagram provide another route that only becomes clear at the end.
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.
Will Tudor plays both Aiden MacNeil and Algernon Marsh, connecting the two story worlds.