The Ringer [Guy Hamilton, 1952]:
Modern audiences will guess the identity of the titular "The Ringer" within the first ten minutes, but nonetheless, director Guy Hamilton's feature debut remains a great deal of fun. Based on a 1929 play by Edgar Wallace, this blend of country house mystery, Doctor Mabuse-inspired crime drama and wry comedy of manners ably establishes the visual style and thematic concerns of subsequent Hamilton films, such as An Inspector Calls (1954), A Touch of Larceny (1959) and Evil Under the Sun (1982).
Prior to this debut, Hamilton had previously worked as assistant director to Carol Reed [a bit of trivia, in The Third Man (1949), Hamilton was also the camera double for Orson Welles in many of the film's long shots] and the scene where Denholm Elliott's character is pursued across the rooftops of Piccadilly shows a definite influence from both The Fallen Idol (1949) and the aforementioned The Third Man respectively.
The cast is excellent here. As well as the then-fresh-faced Denholm Elliott there's also Herbert Lom, Mai Zetterling, Greta Gynt, and the original "Doctor Who" himself, William Hartnell. Already we're seeing Hamilton's propensity for large ensemble casts made up of huge stars and well-known character actors.