Kim Jun is the best deep sea diver in the South Korean Navy’s rescue unit. Along with childhood friend Tae Hyeon, Jun had joined the Navy, where they both fell for Kang Su Jin, although it’s the free-spirited Jun who gets her. When Jun accidentally discovers that his buddy Tae Hyeon also has feelings for Su Jin, Jun resolves to save the friendship by cutting all ties with Su Jin, even though he really loves her.
Fast-forward to 3 years later, Jun and Tae Hyeon are still good friends and Lieutenants in the Navy. But the status quo is shattered with the return of Su Jin, who has come back to command their unit.