Nine teenage girls are en route to Hawaii when their plane fails, leaving them stranded on a remote island. Among them we meet Leah, who has survived to tell their story to a pair of federal investigators. Flashbacks offer an intimate look at Leah’s pre-island life, and the taboo relationship that broke her heart.

The castaways are still reeling after a tragic event. Frustrated by everyone else's inaction, Rachel leads an expedition to the island's summit to get a lay of the land. We learn more about her career as an elite athlete, the extreme measures she's taken to succeed, and the brutal truth that she isn't sharing with the others.

When one of the castaways goes missing, a search party heads out to find her. We learn more about Fatin's past, which isn’t exactly the glamorous thrill ride the others thought it was. At the end of their exhausting day, the girls make a shocking discovery that stokes Leah's doubts about the island.

A tidal surge forces the castaways to relocate their camp. Still suspicious of the island and how they got there, Leah turns her paranoia on one of the other girls, viciously accusing her of knowing more than she's letting on. In flashback, Jeanette's astonishing backstory is unveiled.

Assuming that rescue is imminent, the castaways let loose. The only girl who doesn't feel festive is Shelby, and a look into her past reveals why.

The stranded girls grieve one of their own. Meanwhile, we learn they’re not the only ones ensnared in this social experiment—it turns out there’s a male control group, marooned on a different island.