During a festival in Ninjago City, a group of masked and robed thieves break into Cyrus Borg's tower and steal a mysterious red mask. One of them sets off the alarm while they're leaving, and they are intercepted by Lloyd, only for their leader to escape with the mask. At Lloyd's instruction, P.I.X.A.L. reaches out to the rest of the Ninja in order to reunite the group, first reaching Nya after she has defeated a trio of warriors oppressing farmers. Cole and Jay visit a monastery in search of Sensei Wu, who has been missing for a year, only to get into an argument after finding him absent.
Kai and Zane are reached while battling The Mechanic, and after subduing him the group reunites at Borg Tower, where they learn that the thieves are a crime syndicate known as the Sons of Garmadon. They are also introduced to Hutchins, who explains that the stolen mask is one of three, with another being in the possession of Ninjago's Royal Family. The Ninja are called upon to provide security during a speech by the Emperor, during which Lloyd acts to protect the Empress and Princess Harumi from what turns out to be a firecracker. In gratitude, the Ninja are invited to stay at the Royal Palace while the threat remains.
The Ninja are then introduced to the royal family, during which it is revealed that Harumi was responsible for the group being invited to the palace and that she is an adopted member of the Royal Family. Hutchins then shows the Ninja around the palace, concluding with the display case containing the Mask of Deception. Hutchins reveals that the stolen mask was the Mask of Vengeance, while the Mask of Hatred's location remains unknown. Later, as the Ninja are guarding the palace during the night, Lloyd checks on Princess Harumi-in whom he has shown obvious interest-only to find her room empty and a door to the outside open.
This is the first episode in which Lloyd will be properly voiced by Samuel Vincent, indicating that the character had finally gone through puberty; the other Ninja comment on his voice during the episode.
When the Sons of Garmadon are stealing the Mask of Vengeance, a gold statue resembling Khanjikhan is visible in Cyrus Borg's collection.
Cole and Jay hold a conversation about how time travel could alter reality to the point of people changing in appearance and not even realizing it; this serves as an explanation for the Ninja now resembling their counterparts from The LEGO Ninjago Movie.