When Liv lands an all-expenses-paid opportunity to study aboard the luxury cruise ship the Eos for a semester, she can't believe her luck. Especially since it will offer her the chance to spend time with Will, her ex-best friend, who's barely spoken to her since the night their relationship changed forever.

But as soon as she steps on board, Liv realizes just how out of her depth she is. With Will, with the rest of the Seamester students - including the brittle and beautiful Constantine, who may be hiding his own ties to the Eos - and most of all, with the Sirens, three glamorous and mysterious influencers who seem to have the run of the ship. Liv quickly discovers that the only reason she was invited to join the trip is because another girl disappeared shortly after enrolling-and no one seems to know what happened to her.

When further disappearances rock the ship and strange creatures begin haunting Liv's dreams, she wonders: Is the Eos hiding a dark secret within its shadowy decks? The truth will come at a price, only, how much is Liv willing to pay?