This was the musical episode of Grey’s Anatomy.  The episode starts with Callie and Arizona post-car crash.  Callie is severely injured, and all of the doctors work to keep both her and the baby alive.  Addison Montgomery flies in to help out.  Ultimately, Cristina figures out the best surgical option, which alienates Teddy.  Both Callie and the baby survive, and Arizona and Mark finally realize that they both belong in the baby’s life.  Callie eventually recovers.  

Meredith emotionally explains to Derek about how she was jealous of Callie for getting pregnant.  Derek promises Meredith a baby.  Lexie seems to waver and consider going back to Mark, but Jackson and Lexie end up going home together.