The Samurai Rangers must seal up cracks in the ground where water from the Sanzu River is seeping in. Meanwhile, Arachnitor resurfaces and uses the water to prevent himself from drying out. At the Shiba House, Antonio works on the Black Box. After he completes it, he rushes to where the other Rangers are. The Rangers battle Arachnitor and Antonio finally makes it there. He informs Jayden and the others that he has finally unlocked the Black Box. Jayden uses this new power to access his Super Mode and defeat Arachnitor. Once Arachnitor grows into a mega monster, they use a new cannon to destroy Arachnitor.
The Rangers must defeat Armordevil, a hard-shelled Nighlok who proves to be a formidable opponent. Meanwhile, Antonio loses his Samurai Morpher without realizing, and the two wannabe Samurais (Bulk and Spike) find it. The Rangers combine their attacks in a certain order to weaken Armordevil's shell, and Kevin uses the Black Box to finish the Nighlok. In MegaZord mode, Armordevil's shell is fully restored, which proves difficult to break. The Rangers then repeat their first method of defeating Armordevil, but still is ineffective. The Samurais call the Claw Zord for the Claw Armor MegaZord, then the Samurai Battle Cannon, and finally finishes the battle once and for all. Afterwards, the wannabe Samurais put the morpher in the exact spot they found it. Mike and Emily show up moments later, relieved at Antonio's safety, and return his morpher from the ground. Antonio wonders what he missed all day.
A new Nighlok named Switchbeast traps the spirits of four rangers while Mike and Emily try to defeat him to save the others. Jayden is a garden-gnome, Kevin a ballerina music box, Mia as a fan, and Antonio (ironically) a fish he was going to eat. Switchbeast also traps the spirits of people at a public market in some of the items they were selling- including the wannabe samurais. Switchbeast does this to have the humans recycle his victims without knowing it, which will cause the misery of the people he switched to raise the Sanzu River. Mike and Emily manage to switch the Nighlok's spirit with Mike to make him force the spirits of everyone back into their own bodies. This works as even the Samurais return, but Antonio is traumatized when he escapes just as a stray kitten is about to eat the fish he was in. Mike goes Super Samurai and destroys Switchbeast, but with the Nighlok supersized, the two rangers must pilot their Claw Armor Megazord. The two rangers win and celebrate with their friends by having a bar-b-que. Meanwhile, Xandred is angered at this defeat, and throws a Furry Wart out a gap. The Furry Wart meets Dayu on a river stream as Dayu plans to find a way to end Master Xandred's life for casting her out and breaking her harmonium.
A depressed Antonio sits in front of a lake when he gets a distress call from Jayden, stating they need his help. While the Rangers are fighting some Moogers, Antonio appears and Morphs. He pulls out the Barracuda Blade, and cringes in fear at the sight of it. After the Moogers are defeated the Rangers make sure Antonio is okay and Antonio reveals he's scared of fish. Meanwhile at the Sanzu River a new villain, Serrator appears and offers help to him in his plans. Master Xandred is skeptical at first but when Serrator proves his loyalty to him he is accepted. Back at the Shiba House the team tries to help Antonio out with aversion therapy, Jayden is afraid of spiders, Mike is claustrophobic, and Mia is afraid of frogs. After that attempt fails, the Gap Sensor goes off and the Rangers rush into action. Antonio stays behind, and Ji shows him the Lightzord, an ancient Zord that no Ranger has been able to master and Ji asks Antonio to see if he can unlock it. The rangers deal with two Spitfangs before Serrator destroys the monsters and personally tests the Samurai rangers' fighting skills. Serrator effortlessly defeats the Rangers in battle. At the last second, Antonio arrives with the Lightzord to drive Serrator off before enlarging Lightzord to take out the Papyrox. Later on the Rangers ask Antonio how he got over his fear, he tells them and they laugh.
Jayden and the team must track down Antonio and Mentor Ji after they get kidnapped by Octoroo, Moogers, and Eyescar.
A boy named Cody unleashes the first Samurai Zord called the Bullzord (which has been guarded by Cody's family since its first appearance), which runs amok across the countryside, causing the Rangers to find a way to catch the Bull Zord and get it under control. Meanwhile, Serrator sends Crustor to capture the Bull Zord so that he can use it in an unknown plot.
Mia's younger brother Terry comes to town and tries to convince Mia to sing in his band as part of his performance at a children's hospital. Mia is reluctant to help Terry as her parents want Terry to get into med school. Meanwhile, Serrator begins his next attack on Earth in order to bring his plan into fruition. At the same time, Bulk and Spike try to form their own musical act.
Kevin loses his Samurizer in an attack by the Nighlok Skarf while out in town near the local swimming center where a swim meet is being held. There, he reunites with one of his old swim team members and begins to have thoughts that he should return to swimming, as his friend is not as good as he was, and his Samurizer is still missing. Mike calls Kevin's Samurizer so they can track down Skarf, discovering the Samurizer is in the Nighlok's arm. Elsewhere, Deker and Dayu have made a deal with Serrator so they can serve under him. Dayu and Deker enter the fray with Skarf so Deker may fight Jayden in his Super Samurai mode. However, they end the fight prematurely by destroying Skarf, giving the Rangers the chance to retrieve Kevin's Samurizer. When the Nighlok enlarges, he gains a shield, forcing the Rangers to form the Samurai Gigazord for the first time, with Jayden using Shogun mode to break through the shield and destroy the Nighlok. Later, Kevin goes to the swim meet to see his old friend win after using Kevin's advice.
The Rangers battle a Nighlok that creates mirror images to confuse them. Meanwhile, Spike looks for a job to help out his Uncle Bulk pay the rent.
At the Shiba House, Kevin watches as Emily and Mike train. Kevin tells Emily that she needs to be more tough. Mia tells Emily about a spell. At the Sanzu River, Serrator tells the Nighlok about his new mission.
Kevin and Mike must work as a team when the Nighlok Epoxar glues their hands together.
Serrator, Dayu, and Deker spread paranoia through the residents on the island of Monalua by spreading a special ash from the volcano that induces paranoia. Meanwhile, Master Xandred, Octoroo, and Maldan test their Nighlok Master Blasters in order to turn the tide against the Samurai Rangers.
Jayden has doubts about him having what it takes to being the Red Ranger. Meanwhile, Master Xandred demands that Serrator returns Dayu's harmonium to her.
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. Serrator even unleashes Pestilox upon the city.
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 which will serverly injure the Red Ranger. But when he goes down, another Red Ranger takes his place. Which one is the true Red Ranger?! The answer will change the Samurai Power Rangers forever!
As the Rangers attempt to adjust to being led by Jayden's sister the 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 Samurai 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 Samurai Rangers face off against Master Xandred for the last time.
Master Xandred and Octoroo send Trickster to trap the Rangers in a series of movies.
After battling a humbug of a Nighlok named GRED, the Rangers find themselves stranded inside a malfunctioning Megazord! Will the Christmas spirit, determination and, teamwork be enough to get the Rangers home in time to celebrate the holiday?