Now that Derek has the engagement ring, he searches for the perfect way to propose to Meredith, as Lexie demands that Mark go public with their relationship.

Watch Grey's Anatomy season 5 episode 13 promo

How the big Grey's Anatomy-Private Practice crossover will affect one of Seattle Grace's hottest couples.

Maureen Ryan of "The Watcher" for The Chicago Tribune reports that Battlestar Galactica's Mary McDonnell will be joining the cast of Grey's Anatomy. McDonnell currently portrays President Laura Roslin on BSG.