The Rangers discover that cracks in the earth are now allowing pools of Sanzu River water to seep into our world from the Netherworld and that a mutated Nighlok is using the evil water to keep from drying out as it wreaks havoc throughout the city.

The Rangers struggle to find a way to defeat a Nighlok with an apparently indestructible shell without the help of Antonio, who has unknowingly lost his Samurai Morpher and cannot be reached. Meanwhile, Bulk and Spike find Antonio's Morpher, but think it's a phone that they must return to the original owner.

It's mixed-up mayhem when the Rangers encounter Switchbeast, a Nighlok who can trap people's spirits inside common objects. When the monster does this to four of the Rangers, Mike and Emily must figure out how to defeat him on their own.

After Antonio develops an unusual fear of fish that leaves him unable to be the Gold Ranger, his teammates rally to help him overcome it. Meanwhile, a mysterious and powerful new enemy arrives to help Master Xandred in his quest to flood the earth.

Octoroo, with the help of the Nighlok Eyescar, kidnaps Antonio and Mentor to use as bait in order to lead the rest of the Rangers into a Mooger trap.

A daring boy named Cody unlocks an ancient seal, releasing an enormous BullZord, the very first Samurai Zord, which rampages across the countryside. The Power Rangers must fight to save the city by capturing the beast and taming it to serve as their newest Megazord.

When Mia's younger brother comes to town to try and convince her to sing lead in his band, the reunion is anything but sweet music. Meanwhile, Serrator once again attacks the city.

When a Nighlok eats his Samuraizer, Kevin is unable to help the team defeat the beast, at the same time that he is missing his old life as a competitive swimmer. Meanwhile, Dayu and Deker make a deal with the evil Serrator.

While the Rangers battle a crafty Nighlok who creates mirror images of himself to confuse them, Spike realizes that one of the duties of being a Samurai is to share in the responsibilities of day-to-day life and sets off to find a job so he can help pay the rent on his Uncle Bulk's clubhouse.

Emily has a crisis in confidence, just as the other Rangers are affected by a Nighlok's evil black sand, which sends them into a desperate hunger/thirst mode. While Emily and Mentor Ji struggle to manage the hungry Rangers and defeat the Nighlok, Bulk and Spike find Mia's wallet and head to the Shiba House to return it.

After a Nighlok glues their hands together, Kevin and Mike learn that working as a team doesn't just mean sharing their strengths; it's knowing when they need to ask for help with their weaknesses as well.

Serrator takes the first step in his mysterious master plan to seize the earth by clouding the minds of the people of the island Monalua, spreading paranoia throughout the residents. To stop Serrator, the Rangers will need a special new weapon, the Bullzooka!

As Jayden struggles with his sudden doubts on whether or not he has what it takes to be the Red Ranger, Master Xandred demands Serrator return Dayu's Harmonium, prompting Serrator to reveal his true intentions.

The Rangers discover that Serrator's recent attacks have an ulterior motive -- to crack open the earth and let the Sanzu flood it and thereby become ruler of both worlds.

Halloween gets spooktacular when an evil Nighlok invades the Samurai Rangers' dreams and turns them into nightmares.

When Serrator asks Deker to fulfill the final piece of his destructive plans, Antonio begs Deker to reconsider his role in the battle between humans and the Nighlok.

The Nighlok Fiera unleashes an overwhelming attack on the Red Ranger, but when he goes down another Red Ranger takes his place. Which one is the real Red Ranger? The answer will change the Samurai Rangers forever.

As the Rangers attempt to adjust to being led by a new Red Ranger, Jayden struggles to find new meaning in his life.

Jayden finishes his grand battle against Deker and the other Rangers try to convince him to rejoin their team before Master Xandred reawakens.

With Master Xandred back on Earth, the Rangers finally attempt to use the Sealing Symbol to stop him - only to discover that he has a special new defense against it. Now, they must rise to the challenge and find a new way to defeat him and save the world.

In a climactic battle, the Rangers face off against Master Xandred for the last time.