Stories of Tie Up Games

Two high school seniors or sixth formers girls go scuba diving to de-stress from school, one's a novice. Below the sea, they find sunken money in a sunken boat but a speargun-armed male thug threatens them to surface. They are taken to a different yacht - theirs was destroyed and tight bound and gagged then cast away in an island with scary sounds. How will they escape?

Let me guess, do you have a thing for wetsuit bondage?

This is a request and still open.