Zen and Xander Undone

Zen and Xander are sisters—truly, madly, deeply sisters, and this is their last summer together.
Zen is the "good" girl with a black belt in karate and a newfound penchant for kicking heads. Xander is a wild scientific genius with a self-destructive streak a light-year long. They have three things in common: they're brown-eyed blondes, they've noticed the boy next door has turned into a hottie, and they miss their mom, who died almost a year ago.
These sisters are surviving just fine—except Zen keeps getting into fights that are harder and harder to finish, while Xander spirals into a vortex of late-night parties, scary men, and drugs. What's worse, Xander has scholarships to the most coveted universities in the country, but she's about to ruin everything. Should Zen keep trying to protect Xander, or finally let her go?