The Secret of the Blue Room is a 1933 American pre-Code mystery film directed by Kurt Neumann and starring Lionel Atwill, Gloria Stuart, Paul Lukas, and Edward Arnold.

Thomas challenges Walter and Frank to each spend a night in a mysterious locked blue room in which several murders had occurred years before, each at exactly one hour past midnight.

The next morning, the Commissioner and his assistant Max question the von Helldorfs and their guests, along with Mary and Betty, servants of the manor, and Paul, the butler.

The next day, an apparent vagrant enters the manor, and Robert confesses to the Commissioner in confidence that the man is his brother, who is in fact Irene's biological father.

The cloaked assailant flees into an underground corridor system that runs beneath the manor, with Walter and the Commissioner's officers in pursuit.

[11][12] Beginning in the late 1950s, the film received a revival through television syndication, frequently airing on late-night cable as part of the Shock Theater series.

[16][17] In a contemporary review, Richard Watts Jr. of the New York Herald Tribune found that despite being a bit too formulaic, the film was "better than a number of previous efforts of its school" but contained a "grand cast.

"[14] A review in The Film Weekly similarly observed that the performances by Paul Lukas, Gloria Stuart, and Lionel Atwill were "worthy of a stronger and less threadbare story.

"[3][14] Hans J. Wollstein of AllMovie awards the film a three-star rating, noting that it made "good utilization of standing sets, including the mansion from James Whale's far superior The Old Dark House (1932), adds production values not matched by its Poverty Row competitors, of which there were many.

[21] Writer Bruce Markusen similarly notes in his book Hosted Horror on Television: The Films and Faces of Shock Theater, Creature Features and Chiller Theater (2021) that the actors, particularly Stuart, "handle the material well, especially given the whirlwind six-day shooting schedule imposed by director Kurt Neumann," but felt that it lacked a discernible monstrous villain and resolution for some of its secondary plot elements.