Ho Tae lived in Seoul while he was a trainee for a band on a contract. When he realizes that his agency has been taking advantage of him, he comes down to Busan along with his weak mother to settle down. The movie shows the episodes he experiences while he attends a small band academy in Busan.

While under heavily armed guard, the dangerous convicts aboard a cargo ship unite in a coordinated escape attempt that soon escalates into a bloody, all-out riot. But as the fugitives continue their brutal campaign of terror, they soon discover that not even the most vicious among them is safe from the horror they unknowingly unleashed from the darkness below deck.