Wicked Is As Wicked Does - Wicked, #2

Twins. One whose magic is rigid and constrained, the other's a hurricane of chaos. Serena Covington loves her life. It's full of fun and adventure and she's never bored. Of course, her spontaneity does sometimes cause her spells to go awry, but Serena figures a happy life full of fun is well worth a bit of chaos every now and then. Unfortunately, when a spell curses Serena with restraint, it wreaks havoc on her love life, which means her planned seduction of the ultra-sexy Neil Beckett is now permanently on hold.
Except Neil himself doesn't seem to have received the memo. Under ordinary circumstances, Serena would be thrilled to succumb to Neil's charms, but now she has to wonder whether he's pursuing the real Serena or the new and improved (i.e., boring and restrained) one. If that's the case, Serena knows the relationship is doomed from the start, for when the spell wears off, so too will the romance.