The ninjas ambush a new villain named Miss Demeanor. Nya creates a water cyclone to stop her but loses control of it, threatening a nearby village.
Maya attempts to take charge of Nya's life to solve her problems. Zane and Pixal respond to a distress call at sea.
Nya, Jay, Zane, Pixal and Lloyd board a new submarine, the Hydro Bounty, and set off to find the source of the energy signal disrupting Nya's powers.
Nya and Maya use underwater suits to travel to an ancient temple after they realize its power source is the only way to get the Hydro Bounty running.
Nya and Maya attempt to get out of a tough predicament. Meanwhile, Jay risks his life while trying to restore power to the Hydro Bounty.
After Nya and Maya's rescue, the ninjas are escorted to Merlopia to face King Trimaar. However, a betrayal turns the ninjas into fugitives.
The ninjas survive the palace flooding — but are pursued by ripper sharks. Benthomaar comes to help and leads them to the hangar bay.
A flashback tells the tale of Benthomaar, revealing how King Trimaar finds him as a baby and raises Benthomaar as his own.
The ninjas return to the island of the Keepers and ask their leader to keep an amulet safe in Ninjago City — but they make a surprising discovery.
Kai, Ray, Cole, Wu, and Misako receive Nya's warning and rush to the Explorer's Club. Benthomaar encourages Nya to use her power in a surprising new way.
As Kalmaar and the ninjas wage a battle in Ninjago City, the storm amulet ends up in the possession of a determined paper girl.
Benthomaar tells Nya the tale of Nyad. Meanwhile, Master Wu, Kai, Cole, Ray, and Misako try to keep Kalmaar from taking off with the storm amulet.
The doomsday serpent, Wojira, rises from the sea. In Ninjago City, Glutinous emerges from the water with a dire warning.
The ninjas leap into action after Kalmaar and Wojira arrive in Ninjago City, bringing a tsunami that floods the entire city.
Overpowered by Wojira, the ninjas retreat to the NGTV building to regroup. Nya might make a decision that she may never be able to come back from.
Kalmaar's temper proves too much for Wojira to handle during battle while the ninjas try to help Nya fulfill her destiny.
Watch Ninjago: Masters of Spinjitzu Season 15, Episode 12: Master of the Sea online on FlixGems. Benthomaar tells Nya the tale of Nyad. Meanwhile, Master Wu, Kai, Cole, Ray, and Misako try to keep Kalmaar from taking off with the storm amulet.