It's a decent if unremarkable little mystery with many clichés from that whodunit saturated decade. There's the puzzle of murder in a locked room, an old dark house, and suspects aplenty. Of course, the culprit is exposed amid a climactic assembly of suspects, perhaps the biggest cliché of all. As detective Lance O'Leary (that name should have been reconsidered), actor Purcell has nearly zero charisma, which unfortunately eliminates someone for the audience to identify with. And even the formidable Ann Sheridan is denied her usual pizazz. Only crotchety old Aunt Lucy (Dudgeon) projects real personality. What the movie does have going for it is a clever solution to the locked room.
The studios (here it's Warner Bros.) turned out hundreds of these competent little programmers year after year, a tribute to their professionalism. Of course, a whodunit like Mystery House would migrate later on to TV, especially to a series like Perry Mason (1957- 1966), where the suspects would assemble in a courtroom. Speaking of Mason, catch a sleek, young William Hopper years before his personable detective role on the Mason series.
All in all, the movie's main value may be in it's representative nature of what people went to see on a slow Saturday evening so many years ago.