Archcriminal Paul Barton disappeared seven years ago, and the police think they know where he is: inside a mysterious room-sized cube made of a metal that seems impervious to everything, even a blowtorch. After Perry White informs Clark that Barton will be declared legally dead by noon tomorrow if he doesn't turn up, Superman decides to have a go at it.
It doesn't work, much to the amusement of Barton's brother Steve and his henchman Jody. Superman consults his friend Professor Lucerne, who in the last episode proved that Superman has power over his own molecular density. Lucerne theorizes accurately that Superman can use this same ability to pass through walls. Superman starts passing through the three-foot-thick walls of the cube, but midway there he hears Steve tell his brother that, as "insurance" they've kidnapped Lois and Jimmy and will kill them if Superman penetrates the cube. Superman gives up his effort, but he gets an idea when Steve lets slip that, to make sure that he exits at noon exactly, Paul has a clock connected by radio to the naval observatory time in Arlington, Virginia.
When the time comes, Paul breaks out of the cube ... only to discover he's early because Superman had convinced the naval observatory to mess with his clock. Needless to say, Superman already sprang Lois and Jimmy from their Death Trap before all this happened.
This episode contains examples of:
- Deadly Gas: How Steve Barton plans to kill Lois and Jimmy.
- Dull Surprise: Bruce Wendell as Paul Barton gives one of the flattest villain performances seen in the entire series. Even when he realizes that he confined himself to a cube for seven years to no avail, his expression barely changes. (Then again, maybe it's the
effect of all that solitude...) - Intangibility: Superman is able to adopt this temporarily to pass through walls.
- Kick the Dog: After Superman promises to let Paul Barton go in exchange for Lois' and Jimmy's lives, Steve orders that they be killed anyway for no apparent reason.
- Made of Indestructium: The alloy the cube is made of is totally impervious to Superman's strength, and everything else. Even his X-ray vision can't see through it.
- New Powers as the Plot Demands: For the second episode in a row, Superman develops an ability never used before or since. The odd thing is that the plot doesn't really demand it: Superman actually saves the day through other means.
- Ominous Cube: The titular cube-shaped room was set up to allow Barton to wait out the seven years necessary to be declared legally dead and become a Karma Houdini for his previous crimes.
- Title Drop: Inspector Henderson uses the phrase "the mysterious cube" in the opening segment.
- Verbal Backspace: In the early exposition scene, Clark wonders how Paul Barton could be alone in a cube for seven years without going mad from the isolation.Perry White: That's because you don't think like a criminal, Kent!Jimmy Olsen [grinning]: And you do?Perry White: Of course! ... I mean, I understand criminal psychology!
- Villain Ball: Not only does Paul Barton not have any reason to order Lois and Jimmy killed after he's declared legally dead, but also it would have gotten in the way of his plan of getting away without prosecution. While the police (and Superman) couldn't legally nab him for any crimes he committed before the seven year period, being responsible for the reporters' deaths would mean he could be prosecuted for that.
