This action packed thriller follows a covert Marines unit that once trailed Choi Hee Gon, maritime kingpin of a notorious crime syndicate. Team leader Kwon Jung Ryool was forced to abort his mission after Hee Gon slayed his wife and all the loved ones of the team's original members. Stranded, Kim Sun Woo, Jung Ryool's trusted young agent, has remained undercover. Years later, with Poseidon's reputation and credibility wrecked, Jung Ryool summons Sun Woo from the underworld and together, they set out to take down Hee Gon once and for all. More than a pretty face, Lee Soo Yoon joins the new team as a corporal who is not to be tampered with. An energetic series, Poseidon showcases Lee Si Young's real-life boxing skills.