Note: the sources consulted describe the film's structure and outcome in outline rather than shot by shot, so this analysis covers the confirmed turns without inventing specifics of the culprit's identity.
The film's architecture is a deliberate two-act bait-and-switch. The first movement plays as straight heritage romance with jokes: Eric Noone, a pickpocket, secures a position at the manor under false pretences, rises through the servants' ranks at a speed that no genuine heritage drama would tolerate, and begins a forbidden romance with Rose Davenport, daughter of the house. Crucially, his fraud goes undetected — the film's first real punchline is that the great English household cannot tell a thief from a footman.
The turn arrives with the murder. A body appears, and Eric is framed for it. This is where the comedy's underlying argument surfaces: the household's swift willingness to believe in his guilt has nothing to do with evidence and everything to do with what he is. The hierarchy that failed to detect him when he was actually stealing convicts him instantly when he is innocent. That inversion is the film's sharpest piece of writing and the retroactive justification for the entire first act.
The final movement turns the film into a country-house whodunit played entirely as farce, with Eric forced into the role of detective to clear his own name — a thief compelled to prove honesty. It resolves in a comic showdown that owes more to Airplane! and the Monty Python features than to Agatha Christie. The absurdity of that resolution is intentional: the whodunit's promise that a clever explanation restores order is precisely the genre convention the film has spent ninety minutes deflating. What becomes clear only in retrospect is that the murder was never the subject. The subject was always the house — an institution so committed to appearances that it can absorb a con artist without noticing, then collapse into hysteria the moment appearances crack.