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.