On 31 January 1968, 31 North Korean commandos infiltrated South Korea as part of a botched assassination attempt on President Park Chung-hee. In retaliation, the South Korean military formed a team of 31 criminals on the island of Silmido to assassinate Kim Il-sung in a suicide mission to reclaim their reputation. However, the plan was aborted, leaving the criminals dissatisfied. It is loosely based on a 1970s military insurrection.