The story begins with Morgan Francois, an Ordinary High-School Student going about her business before overhearing her classmate, Julian planning something sinister at a playground. She stakes out until she finds him attempting a kidnapping of a girl who pissed him off, but bungles it. He gives her half of a Glasgow Grin before vowing to call the police on her. The next day, Julian framed her for stalking, assault, and even sending a threatening letter. She is expelled, put under house arrest for half a year, and is branded a pariah. The girl herself is never heard from again.
Six months later, she drives herself two hours away to the backwater town of Wincestre, Michigan. After getting into a fight with a local bully and befriending fellow loser Max, she moves in with her parent's cousin, Marvin. She moves into the garage and falls asleep, but not before finding a mysterious earring. She wakes up in a mysterious chamber headed by a mysterious masked man who declares she now possesses one of the Miraculous. The next night, she meets the attached Kwami, Tundraa, the Arctic Fox.
Just as she tries out her powers, a mysterious abomination battles her on behalf of "the Phoenix Mage", and she narrowly succeeds with the help of Max and his friend, Leon. During the school days, Morgan deals with the Psycho Psychologist Dr. Cho and the Academic Alpha Bitch Kiku. Later, the Guardian gives her the Eagle Miraculous that she subsequently gives to Max. The two of them continue to build up their reputation as heroes. At one point, the two face off against the veteran hero Nevermore as the readers are introduced to the villainous Phoenix Mage himself, secretly CEO Tyler Forrester. He uses the Phoenix Miraculous to create monsters to sow chaos on behalf of his company.
One night, when Morgan invites her friends over while Marvin is away, she accidentally discovers Marvin's reclusive, adoptive daughter, Moof. After she runs off in a panic, Marvin tells how her mother simply vanished and she fell into the abusive hands of Dr. Cho. Morgan saves her from the Phoenix Mage's attack. Days later, Max's mother mails his younger sister, Haley, to attend school there. The Guardian also gives Morgan the Salamander and Mantis Miraculouses, which she gives to Leon and Kiku during intense battles, each. At the same time, The Phoenix Mage is coerced into an alliance by another Miraculer, The Nightmare King. He claims to have "unfinished business" with Morgan.
Weeks later, the school holds a boring fall fest where dozens of students are put under the Phoenix Mage's spell and the four heroes have an epic battle, teaming up with Nevermore. After the battle, the Phoenix Mage only escapes after The Nightmare King holds Moof hostage. After the battle, they find Nevermore critically wounded but he gives them a hint as to how to find The Phoenix Mage.
At the same time, another student, Clay, joins them while using the Jackal Miraculous. During one battle, Morgan is briefly captured by the Phoenix Mage as he explains his own curiosity of The Nightmare King and his own philosophy. Using the tip from Nevermore, the five of them attempt to spy on Forrester's company, Alpha Q, but are caught. The CEO gives them an ultimatum, fight him and The Nightmare King directly in 10 days time, or they're both exposed with the chaos that would imply.
