Three years after solving a high-profile case, uncompromising detective Ma pursues a gang distributing drugs through a delivery app. It soon becomes clear that the case is connected to the largest illegal online casino business, and one of the key figures in this criminal scheme is a former special forces officer: a cynical and ruthless killer will stop at nothing to achieve his goal. But the killer does not yet know who he is in contact with. He will have to compete with the most powerful police officer in Busan.