Iron Vegiemon

The kids answer a call for help from Gabumon, who's attempts to liberate a village of captive Digimon have so far failed, thanks to RedVegiemon, who is under the Emperor's control.

Synopsis
In the Digiworld, Gabumon is helping Gazimon escape from the Digimon Emperor's jail. He is caught by RedVeggiemon and is knocked out cold. Yolei receives a message from Gabumon for help. The DigiDestined ready themselves go, but Yolei is unable to because Izzy is examining her Digivice. Once in the DigiWorld, they disguise themselves as slave Digimon, Gabumon included. They gain access but are once again caught freeing Digmon by RedVeggiemon. Gabumon is unable to Digivolve. Apparently Digimon cannot Digivolve naturally because of the Control Spires. The DigiDestined free the captured Digimon after being horribly beaten by RedVeggiemon. They destroy the mysterious Control Spire in that area. Gabumon is then able to Digivolve into Garurumon and defeats RedVeggiemon. Yolei realizes that the Control Spires power the Dark Rings. The Digidestined deduce that they have to destroy the Control Spire for any particular area to disable the Dark Rings in said area.

Miscellaneous trivia

 * This is the first episode in the series to feature a normal digivolution to the Champion level.
 * The Control Spires, which cause a lot of trouble throughout the series, first appear in this episode.