While Kai is brushing his teeth, he is attacked by three mysterious black ninja. After he gets thrown into the training course, Sensei Wu reveals that they are his students. He performs Spinjitzu and gives them each differently colored Ninja suits to represent their elements: Cole, the Black Ninja of Earth; Jay, the Blue Ninja of Lightning; Zane, the White Ninja of Ice; and Kai, the Red Ninja of Fire. Jay becomes interested when he learns about Nya, though is warned by Kai to back off.
The next morning, they travel to the Caves of Despair to find the Scythe of Quakes. Along the way, Kai questions how the others were fond by Sensei Wu. Cole states he was testing his strength by rock-climbing up a mountain, Jay says he was in Ninjago City testing homemade wings and Zane says he was testing himself by breathing underwater at an ice-cold temperature and in all those scenarios, Sensei was there, drinking tea.
Sensei Wu warns the Ninja not to use the Scythe upon retrieval, fearing they would not be able to handle its power. After stealing back the map that contains the locations of the Golden Weapons, they enter the cave and find the first of the weapons. Upon leaving, however, they are ambushed by Samukai and his Skeleton army. While fighting the Skulkin, Jay mentions that fighting them feels like the training course back at the Monastery, and going through the motions unlocks his Spinjitzu.
Not long after, the other three Ninja unlock theirs as well. When they defeat the Skeletons, they are faced with the Guardian of the Scythe, the Earth Dragon. Unable to defeat it themselves, Kai uses the Scythe, despite the warnings of his teammates and defeats the Earth Dragon, the Ninja barely managing to escape. Outside, Sensei Wu is disappointed that Kai would put the others in danger by using the Golden Weapon.