Jekel Loves Hyde by Beth Fantaskey

"Updates Robert Louis Stevenson's classic story . . . Teens who enjoy brooding love stories will not be disappointed" (School Library Journal).

Jill Jekel has always obeyed her parents' rules-especially the one about never opening the mysterious, old box in her father's office. But when her dad is murdered, and her college savings disappear, she's tempted to peek inside, as the contents might be the key to a lucrative chemistry scholarship.
To improve her odds, Jill enlists the help of gorgeous, brooding Tristen Hyde, who has his own dark secrets locked away. As a team, Jekel and Hyde recreate experiments based on the classic novel, hoping not only to win a prize, but to save Tristen's sanity-and maybe his life. But Jill's accidental taste of a formula unleashes her darkest nature and compels her to risk everything-even Tristen's love-just for the thrill of being bad.

"Fantaskey's latest novel deliberately evokes the doppelganger theme and questionable experiments of Stevenson's The Strange Case of Dr. Jekyll and Mr. Hyde. It also owes a great deal to Stephenie Meyer's Twilight series . . . Fans of the genre won't be able to resist this slick genre update." - Booklist