On the planet of Edenoi, King Lexian grants his grandson Dex the Masked Rider powers before sending him to Earth in a meteor. Upon arrival, Dex's meteor lands in the backyard of the residence of the Stewart family in the city of Leawood. After Dex explains the story of his origins to the Stewarts and why he needs to fit in with the humans on Earth, Count Dregon-the series' main antagonist-sends an Insectivore called the Destructasphere to destroy the city at dawn. In response to Destructasphere's attack, Dex transforms into Masked Rider and prepares for battle.
Dex narrowly escapes defeat at the hands of Destructasphere, and is advised by his grandfather, King Lexian, to create new allies for himself, resulting in the birth of Combat Chopper and Magno. But later, Masked Rider and his new allies must battle a trio of Count Dregon's Maggots when they are unleashed upon the local Leawood High School, as well as the Insectivore Beetletron.
Dex goes to school with the kids and Nefaria has a plan for Count Dregon. Meanwhile, Ferbus stows away in a school bag, and Dex shares some thoughts with his classmates. Then, Count Dregon sends his Maggots to Leawood High. Can our hero stop the enemy's evil plan?
While out on a bug hunt, Hal and Albee encounter an Insectivore named Mothitron, who attempts to transform them into Insect Soldiers loyal to Count Dregon. Masked Rider must defeat Mothitron as well as discover an antidote for Hal and Albee's growing mutation.
Albee is challenged by a bully to a video game play-off, but his reluctance ultimately has Dex filling in for him. Meanwhile, Count Dregon unleashes an Insectivore named Crimson Creeper to battle Masked Rider.
Dex's friend Donais comes to Earth on a mission to upgrade the Masked Rider powers to "Super Gold", but Count Dregon kidnaps Donais and uses the upgrade crystal meant for Dex to turn Donais into the evil Robo Rider.
The kids start a clean-up campaign in Leawood and it's just another day at the office for Count Dregon. Then, Nefaria supervises a little cleaning herself. This gives Cyclopter another idea for an evil monster. Can our hero stop the monster?