Flash Gordon Conquers the Universe returned to Alex Raymond's comic strip for inspiration. It draws upon the celebrated "Ice Kingdom" story arc from the spring of 1939. The screenwriters also appropriated a character who had appeared earlier in the comic strip--Sonja. She would become the serial's requisite bad girl, following in the footsteps of Princess Aura in Flash Gordon and Azura, Queen of Magic, in Trip to Mars. While the comic strip Sonja threw herself at Flash, the serial's Sonja follows the chaste attitude of Trip to Mars. Sonja isn't interested in Flash. She's just interested in serving Ming.
Conquers the Universe also brings back two characters from the previous serials: Princess Aura and Prince Barin, who are now happily married. In the person of Priscilla Lawson in Flash Gordon, Princess Aura chased Flash unabashedly. But Anne Gwynne in Conquers the Universe is given the unenviable task of playing a colorless Princess Aura. Any fire in the eyes of the original Aura has long been replaced by blissful complacency. And while Prince Barin was played by the balding, portly (but powerful) Richard Alexander in both Flash Gordon and Trip to Mars, in Conquers the Universe, Barin suddenly loses 50 pounds and most of his muscles. In comparison to Alexander, Roland Drew's Barin looks meek and hardly capable of corralling the troublesome Aura.
While Conquers the Universe follows the pattern of Trip to Mars by eliminating creatures and utilizing ample stock spacecraft footage from Flash Gordon, it also benefits from a change of locale. For several episodes, Flash, Dale, Prince Barin, and Doctor Zarkov brave the chilly conditions of Frigia--a frozen land in Northern Mongo. This sequence provides one of the best cliffhangers of all serialdom: our heroes are caught in an avalanche as they attempt to scale a mountain. Well-integrated stock mountain-climbing film footage shows climbers being hurled down mountain slopes. Eventually two people slide over the edge of a crevasse. We hear Dale scream as they fall into the crevasse's shadowy depths. How can they survive? Of course, they do survive, but by 1939, serials were widely lying to their audiences. A fall over a crevasse in one episode becomes nothing more than a close call in the next chapter. But in Conquers the Universe the serial makers play fairly: Flash, Dale, Zarkov, and Barin do indeed fall into the crevasse and they barely escape with their lives. As the episode opens, Flash slowly rises from a bank of snow. Stunned, he shakes his head and brushes snow off his shoulders. He eventually arouses Zarkov and Dale, but Barin is seriously injured. And soon afterwards, we're given a doozy of a development as Ming sends mechanical men after our heroes. With spastic motions and foot-long fingers, the robots lurch across the frozen terrain.
In addition to the mechanical men, Conquers the Universe also features a race of men from "The Land of the Dead" who wear costumes that make them look like pointy-headed walking rocks. Unlike most serial characters, they don't speak English. They speak an obscure, strange-sounding tongue. Their speech is realized by playing their dialogue backwards. (Of course, Zarkov not only identifies the language of the Rock Men -- he can speak it!)
While Conquers the Universe is generally considered the weakest of the Flash Gordon serials, it's preferrable in many ways to Trip to Mars. Its cliffhangers, for example, are a noticeable improvement. Neither sequel comes close to capturing the delirious excesses of Flash Gordon, but these are superior examples of the American serial form.