Abandon book 1 of 3, completed series

Pierce knows what it's like to die. 

Last year she flatlined following an accident. During that time Pierce saw a dark world and met a mysterious irresistible boy.

Now that boy, John Hayden, has turned up at her school. Every time she sees him Pierce finds herself in terrible danger. Yet she's still drawn to him.

John wants to take her back to the place she fears the most: the Underworld.

The question is, why?