An interesting whodunit that suffers mainly from flaws in motivational logic for the characters, as well as unbelievable legal procedures, but that is part of the sense of disbelief that has to be suspended for many B-movie crime dramas of the era.
Lionel Atwill is the state executioner, who needs his job to finance his research which is ironically, brining the dead back to life. He gives a brief explanation of his process theory, though it isn't important to the story. He feels he has to keep his job though because of the importance of it to his work, particularly financing it, despite the fact that his fiancée finds the job abhorrent and refuses to marry him when she finds out what he does.
In the opening scene you have seen her walking to the death chamber, with the story told in flashbacks by the detective played by Cy Kendall. Lionel Atwill's character you figure out early is in the unenviable position of being required to pull the switch on his girlfriend. As time is running out, Kendall tries to gather evidence to clear her.
Since it is told in flashbacks, some things that are to happen you learn early on, but the film telegraphs too much that it doesn't intend you to know, at least not for sure. There is never even the slightest doubt about who is innocent or hiding something, and the movie would have benefited from a little more ambiguity in the beginning, which could have been easily accomplished. With a little work on the script, this could have been a much better movie.
All in all not bad, and with a runtime of 56 minutes doesn't have time for you to grow weary waiting for the solution.
One aspect that seems amusingly dated today though is the crime Mary's father was convicted of when she was a child: Pinball racketeering. Largely forgotten now, but there was a time when pinball machines were a dreaded, evil scourge that many cities tried to stamp out with bans. Her father was railroaded by an aggressive district attorney, and for the purposes of the movie, it provided a "criminal" father who actually wasn't too bad, and was perhaps unfairly persecuted.