After three years of prep, Kim Minsu is ready to start his first day as a guard on the XB-880, a high-security prison in the middle of the ocean. On his first day, the prisoners riot and take over the ship. As they massacre the guards, Minsu poses as a criminal to survive. Though wary of this new face, he is accepted as one of them. Now, Minsu has to maintain this ruse until help comes, but as a powerful faction takes hold of the brig, he must work with the other inmates to fight for control.