Octavia's life as a broken cripple ends in a park when a mad clown-girl bombs the Trio of Albion, leaving her best friend Willow wounded. Arrested and trapped in a DC interrogation room, Octavia is prepared to commit suicide to protect Willow's secrets when a black-ooze zoog, Nerys, offers her a pact. Drinking the ichor, she becomes a magical girl. The first manifestation of her power is visceral: when a Section Special officer tries to subdue her, she punches his skull into a fine red mist. Pursued by the Trio, Octavia is stabbed through the gut by Scarlet Edge, but in a final act of defiance, she bites the magical girl's face, claiming her first scar on her enemy. Nerys rips a hole in reality, and Octavia is dragged to the moon.

Now a fugitive on Plato Base (a Nazi moon base turned rebel stronghold), Octavia meets the other magical girls: the psychotic clown Grimgrave, the obsessive dragon Burning Bright, and the techno-witch Signal. But her obsession with Willow is a glaring flaw. Discovering she hasn't truly transformed yet, Octavia breaks out, translocating back to Earth alone. After a brief, tense reunion with her grandmother (who poisons her on DC's orders), she staggers to her parents' grave. There, the occultist Winter saves her from dream-cats, but it's a trap. She rushes to the hospital to save Willow, only to find her "best friend" is a lucid Dreamer who has been manipulating her for ten years.

Willow tries to re-enslave Octavia, but Grimgrave's shotgun blast interrupts the ritual. The Trio of Albion arrives to capture the "defective" Dreamer, but the Luna rebels—Bright, Signal, and Grimgrave—translocate to the rooftop in a televised intervention. In the chaos, Octavia experiences a desperate half-transformation, landing a devastating punch on Scarlet Edge and reversing the Trio's dominance. But the moment is shattered when Willow intervenes; Scarlet's sword cuts Octavia's prosthetic arm in half, and she suffers a heart attack. Grimgrave drags her away to Luna as the battle is filmed by the crowd, shattering the magical girls' illusion of invincibility for the whole world to see.

Recovering on the moon, Octavia is a wreck of grief and rage, realizing that her love for Willow was a fabrication. She attempts to masturbate, only to trigger a heart attack, forcing Grimgrave to revive her with a kiss. After a tense confrontation with Bright (who is obsessed with Scarlet Edge), Octavia finds a mission: repairing her arm. While the others hunt a Nightmare to refuel their magic, Octavia designs and 3D-prints a new, upgraded version of her prosthetic. In a late-night revelation, she discovers Scarlet Edge has been drawing beautiful portraits of her and secretly contacting her via an encrypted app. The conversation turns obsessive, with Scarlet revealing her "mundane" name and a desperate desire to be "owned" by Octavia, promising to duel her again to give her a "clean death" rather than see her returned to Willow.