After being disowned by their adoptive parents, Ah-hyun and the kids live as if they are dead. They endure brutal training, determined to protect themselves. Meanwhile, Tae-sik, who has been secretly rescuing children from the malicious organization, makes a bold decision to save a new "refund" target.

To put an end to the inhuman adoption and refund system, Ah-hyun and the kids set out on a daring mission to confront the head of the evil organization. With fierce determination and a carefully crafted plan, they infiltrate the organization's bunker to strike from within. But once inside, Ah-hyun uncovers a devastating truth behind the system.

The kids risk their lives to save their guardian, Ah-hyun. To do so, they're in desperate need big money, forcing them to confront Ju-an's adoptive father. Their plan is to steal offerings from his church. Meanwhile, Se-hee's ambition to seize even greater power pushes her toward devastating choices that could change the world.

Framed for murder, Ah-hyun and the kids turn to the only adult they trust, Detective Choi. Meanwhile, the unexpected and unwanted return of of Seok-su, the adoptive son who was believed to be dead, throws Kwon Kang-man into a crisis, leading him to seek ways to put an end to the adoption on his own.

The kids barely make it out alive from the fire, but with a tragic loss. Fueled by grief and rage, they vow revenge against the monster once more. Meanwhile, Kim Se-hee sets her sights on a refund project that is far more massive, ruthless, and shocking than Ah-hyun and the kids could have ever imagined.

What begins as a camping trip soon turns into a living nightmare. Kim Se-hee's inhumanity reaches its peak as she executes her plan to massacre the "defects." To stop her once and for all, Ah-hyun and the kids rise up against her and her team, risking their lives for all the lives to avenge the ones already lost and protect those who could be next.