Junsu, a public health doctor serving his mandatory term at Songhwa Prison, thought his assignment would be dull, routine checkups, a few minor injuries, nothing more.

But on his seventh day, the world literally collapses. A mysterious nationwide sinkhole disaster swallows cities whole, cutting the prison off from the outside world. Now trapped inside a fortress filled with men more terrifying than demons, Junsu has only one thought:

“I have to get out of here.”

Clutching a stolen keycard, his only ticket to freedom, he makes a break for it. But before he can escape, he runs into the infamous Lee brothers, Tae-hyeong and Tae-mu, cold-blooded criminals whose names alone strike fear even among inmates.

“What a feast. Lick it clean.”

With monsters above and monsters within, Junsu’s fight for survival turns into a chilling game of instinct, trust, and the brutal will to live.