The allied forces gather on a cliff not too far from Mingo City. Flash only wishes that they could have some kind of information from inside, and gets his wish when Zarkov contacts him through an "astral projection" device belonging to Ming. He tells them that whatever they do, they should do it quickly, as Mongo is nearing Earth; what's more, Ming has grown tired of Arboria's guerilla war against him, and has decided to crush it with flying war machines, and an even greater danger from below. Before he can explain the nature of the attack, though, he is cut off by Ming, who laughs at them and ends the transmission.
They are forced to make a detour, finding Arboria under attack. However, Arboria's forces seem to be greater than Vultan's - great enough to stand off Ming's flying navy in another explosive battle. While they celebrate, it turns out that this was only the prelude: Arboria is also under attack from underneath, with giant drills piloted by Ming's Mole Men attacking the trees of Arboria through their roots, and thus slowly killing Arboria itself. As it turns out, though, they are hardly defenseless on this front, either. In addition to ordinary warfare, they are able to manipulate the trees' roots, fighting back against the mole men, subduing them and allowing the Arborians to take them prisoner - and the drill machine with them. With this drill, they come up with a new plan: To send themselves, and a few of their best warriors, into the heart of Mingo City - where an army would fail, a few might succeed.
Ming is not idle. He forecasts his conquest of Earth, claiming that it was foretold long ago that he conquer the universe, and that Mongo and Earth will be united not only by conquest, but marriage. Doctor Zarkov is left in despair as Ming continues to his harem, and taking Dale by the hand, declares that she will become his bride, forcing his will on her own, hypnotizing her until she agrees to obey him. They are both brought before a Mongan priest, who calls upon the Mongan god Tao and begins the ceremony.
Those piloting the drill continue their underground journey. They are waylaid when they are caught in a vein of magma, but it is a momentary setback; Flash is able to get their traction again, and they continue all the way to Ming's palace, bursting through the floor moments after the ceremony is completed. Their small but elite force pours out of the vehicle, turning the hall into a battlefield. Ming flees into an elevator, dragging a still-confused Dale with him. Flash follows - Aura throws a spear at the hero, determined not to let him be with Aura; Thun makes an incredible midair catch, saving Flash while Barin accosts the princess, again declaring his love - and Zarkov follows Flash in his chase.
As the conflict rages behind them, Flash forces open the elevator doors, and together, they follow in Ming's footsteps into Ming's underground inner sanctum. Fighting past a few more Metal Men, they confront Ming. They are too late, he insists; in but a few minutes, Mongo will be approaching Earth. Flash disagrees, beckoning. Ming attacks him in a rage, wielding a flaming sword, as Mongo and Earth draw ever closer together. Even Mongo does not get off lightly, and there is no telling what must be happening to Earth as Flash fights Ming in its defense, finally knocking him off-balance with a piece of debris, sending the sword flying from his hand. It skids toward Dale, who - fighting the effects of Ming's mind control - raises it up and brings it down on the machine controlling Mongo's path.
The near-miss is ended. Mongo continues in its path, with Earth being left far behind. Flash, after dealing Ming a flying tackle, is reunited with Dale Arden, kissing her in celebration. Earth is saved... but Ming, adamant, declares that this is only a minor setback. He reveals that he is immortal, and can afford to wait; meanwhile, the Earthlings are now separated from their home planet forever. He activates a device and teleports out of there, sure to return with greater forces. Flash is more optimistic, certain that Zarkov will be able to fix that problem and get them home, and they leave the scene together. Ming, ever confident, simply laughs...