Kai grew up dreaming of becoming a blacksmith like his father. But that was before skeleton warriors ransacked his village and abducted his sister Nya. Now he's training to become a ninja master of spinjitzu in this Lego martial arts saga.

Long ago, the Four Golden Weapons of Spinjitzu were created by a great warrior who created Ninjago, the First Spinjitzu Master. When he passed away, his sons were tasked with protecting them but the older brother was consumed by evil and became Lord Garmadon, determined to use the weapons to reshape Ninjago in his own image. Sensei Wu was forced to banish his brother to the Underworld and hide the four weapons with dragons as guardians. However, Lord Garmadon has recruited an army of skeletons to find the map that will lead them to the four weapons. Sensei Wu needs Kai, Zane, Cole and Jay to use Spinjitzu and the Tornado of Creation to find the weapons first. Only then will the world be safe.

A solitary wanderer meets Kai, a young sword-maker, and his sister Nia in their small farming village right before a terrifying skeleton army arrives, ransacking their shop. The army takes a map hidden by their father years ago and Nia! The wanderer turns out to be Sensei Wu, an old friend of their father's. He promises to help Kai find his sister, but first Kai must become a ninja and master the art of spinjitzu. Kai begins his training and soon meets Sensei Wu's other ninja's, who realize they've all been recruited for very specific skill sets. Long ago, four weapons of spinjitzu were created by a great warrior. When he passed, his sons were tasked with protecting them. However, the older brother, Lord Garmadon, wanted to use the weapons for his own powerful and evil intents. Sensei Wu was forced to banish his brother to the Underworld and hide the four weapons with dragons as guardians.

A solitary wanderer meets Kai, a young sword-maker, and his sister Nia in their small farming village right before a terrifying skeleton army arrives, ransacking their shop. The army takes a map hidden by their father years ago and Nia! The wanderer turns out to be Sensei Wu, an old friend of their father's. He promises to help Kai find his sister, but first Kai must become a ninja and master the art of spinjitzu. Kai begins his training and soon meets Sensei Wu's other ninja's, who realize they've all been recruited for very specific skill sets. Long ago, four weapons of spinjitzu were created by a great warrior. When he passed, his sons were tasked with protecting them. However, the older brother, Lord Garmadon, wanted to use the weapons for his own powerful and evil intents. Sensei Wu was forced to banish his brother to the Underworld and hide the four weapons with dragons as guardians.

Jay takes Nya for a ride on his dragon, Wisp, to pick up some things she needs at Four Weapons.