Commander Beag sacrifices himself the save the Tenkai Knights from falling down into a canyon, causing them to develop a new Robofusion. They soon find out Beag is trapped in the Valley of Secrets and go to rescue him. They also find the fifth and last Dragon Cube inside the Valley.
On Quarton, the Tenkai Knights and Corekai face off against Slyger in a valley with a steep canyon at their backs. When Valorn tries and fails to transform into Titan Mode, he almost falls into the canyon below, but is rescued by the Corekai. Toxsa and the others are attacked again and nearly fall again in until Commander Beag selflessly puts himself in danger to save him. As the Knight's try to think of a way to save Beag and his two men, Slyger attacks and Beag and his men sacrifice themselves and all three fall into the canyon.
When the boys arrive back on Earth, Mr. White notices something is wrong and the boys tell him of the loss of Beag. Boreas appears and tells the boys about the valley they'd just been fighting in, calling it the Valley of Secrets. He explains that one time long ago another group of Corekai were lost there. He further explains that the original Tenkai Knights went searching for there comrades and found and rescued them.
The next day at school, Chooki and the others discuss the upcoming basketball game, but Toxsa complains, noting they should be focusing on trying to locate Beag. Guren agrees that Beag is an important member of their team, and that even the rouge Knight Dromus may have an important part to play. At that moment, Gen walks by and Guren asks him if he'd like to join their team. Gen instead walks away without answering.
After practicing basketball until school gets out, the boys head straight for Mr. White's shop. On Quarton, the Knights learn that the other Corekai have been unable to find Beag and his men. Despite the news, the Knights are still determined to find there missing friends. While searching the Valley, they stumble across a hidden temple. When they attempt to investigate they keep setting off traps and despite the setbacks, they soon find Beag and his men are alive, and have even located the fifth and last Dragon Cube inside the temple.
Upon escaping the temple, they are again attacked by Slyger. Beag gets hit by Slyger while trying to protect the cube and his men put themselves in danger to save him. Beag and his men again fall into the canyon. Only this time, Bravenwolf and the others jump in after them. Guren explains that he plans on all of them Robofusing together. Guren's plan works, as the two groups fuse into both the Protojet and the Air Lancer Jet at the same time and defeat Slyger and his men.
In the episode
- This episode reveals that the Corekai can join the Tenkai Knights in Robofusion.
- Dromus appears again in this episode.
- The Air Lancer Jet first appears in this episode as the Knight's second stage two Robofusion jet.
- This episode proves that Dromus works for the Corrupted as he told Slyger and his army of Corrupted to retreat.
- This episode first shows 2 Robofusions of the Corekai to fight the Corrupted.
English Dub Cuts & Changes
Note: All characters are listed in order of their first appearances in the episode. The time they appear is the time from the Japanese dub.