The Monastery is under heavy siege from Skeletons, which mined Maelstrom Ore from Crux Prime to forge new weaponry that is immune to most spinjitzu attacks. This increased the Skeletons' health to the point where it began to overwhelm the Ninjas.
The Monastery was originally set upon a high mountain, and a chunk was broken off by the Skeletons and thrown into space. Sensei Wu was able to pilot this to the beacon from Nexus Tower, crashing it into Crux Prime. Skeletons followed Wu and discovered the Maelstrom. With it, they were able to return to the Monastery to attempt to deal the final blow and find the Golden Weapons of Spinjitzu. The Nexus Force, now having made friends with Sensei Wu and knowing that Nexus Force gear can smash Maelstrom enemies, but it cannot smash skeletons very well, send players to help defend the Monastery. Learning the art of Spinjitzu from the four Ninjas trained by Sensei Wu (Kai, Zane, Jay, and Cole), players are able to embark on a massive mission chain, defeat the skeletons, recover the Golden Weapons, and take back the Monastery.