O slips out of a gloomy, robot-run orphanage at night, Miss C on his shoulder, and sets out to find his biological parents. He drops into the dark forest and starts down the path — until twigs snap behind him. He stops cold, peers into the black between the trees, and calls for whoever's there to come out.

The thing trailing O reveals itself: Cash, a bored, slouching ghost who claims he's only tagging along to keep the boy safe. Then Zack, a cocky vampire, slams down out of the sky and warns O that Cash just wants his soul — while pitching himself as the real protector. The two are soon nose to nose, arguing over O's head as he stands frozen between them.

As Cash and Zack keep squabbling over who gets to protect him, O cuts in and realizes both of them want something from him. He offers a deal: help him find his parents, and afterward they can each have whatever they're after. The two agree and the trio heads off into the trees — Cash already whispering his plan to get rid of the vampire.

O opens up about growing up alone among the orphanage robots and his resolve to find his real parents. But when the sun rises, Zack and Cash scramble for cover — daylight is deadly to a vampire and a ghost alike. O reluctantly accepts that the group can only travel by night.

At nightfall they push deeper into a forest strewn with the overgrown ruins of human civilization. Cash and Zack bicker over who gets to explain what happened to the world. Then Miss C senses they're being followed — and a massive black shadow rises from the bushes.

The shadow turns out to be Zombie Friend, a slow, easily distracted undead in a sharp suit. He insists he only wants O's brain, but stuns everyone by instantly seeing through Cash's and Zack's hidden schemes. Then he drops a bombshell: he knows where O's parents are.

Zombie Friend reveals he's been eavesdropping the whole time — thanks to a rotting ear stuck to the bottom of O's shoe. Miss C sizes him up and gives her approval for him to join. But his lead comes with a catch: he doesn't know exactly where the parents are, only where he last saw humans like O.

Trudging along at Zombie Friend's painfully slow pace, the group finally reaches his destination — a decaying, overgrown amusement park. He leads them to a crumbling attraction whose broken sign reads only "THE HOUSE OF MIR..." Inside the dark maze, two menacing shadows begin swelling across the walls.

As the shadows close in, Zack pieces together the busted sign from outside and bursts in with the answer — they're just warped reflections in a funhouse mirror. Relief turns to confusion when O and Zombie Friend admit they've never even heard of mirrors. Then a raspy voice cuts through the dark, claiming the place isn't a house of mirrors at all — it belongs to someone named Mir.

O notices that not everyone in the group casts a reflection — and without warning, Miss C leaps straight through the rippling glass. O dives after her into the Mirror World, a pristine white dimension where liquid silver rises up and forms into Mir herself. She welcomes him with an unsettling promise: here he'll learn the truth about everything, including his own.

Mir tells O the only way to his truth is to face his own mirror, then raises five of them from the floor — one for each of them. O passes through his easily, but Cash smacks into solid glass: everyone has to enter alone. One by one, the companions pick their mirrors and step through, each vanishing into a private test.

Separated inside the mirrors, each companion finds O offering them exactly what they've always wanted — his brain, his blood, his soul. Whether any of them gives in stays hidden as they reunite in silence, secrets intact. Mir hands the real O his Miss C and declares the tests over: he's finally ready to know the truth.