Libra Ascending by Tricia Barr

Twelve teens. One Task. Save the Universe.

Brielle has never been normal – she sees things no-one else does. But as it looks like she’s about to be adopted after growing up in an orphanage, she’s the closest she’s ever come. All she has to do is act…well, normal.
The new guy in town, Tristan, is anything but that. On the first day she meets him, he starts talking to her of visions and aliens and a darkness so evil, it will take twelve Zodiac heirs to defeat it. Brielle knows she should run the other way, as fast as she possibly can.
If only she wasn’t so undeniably drawn to him…
When assassins attack and Brielle can no longer deny she has powers, she begins to wonder—is Tristan telling the truth? Are there others like her? Are her feelings so powerful because she and Tristan are soulmates?
And ultimately, will Brielle have to sacrifice everything she’s ever wanted so she can join a daunting fight to save the universe?