Last week's Addison-to-Derek phone call was just a teaser: The real Grey's Anatomy/Private Practice crossover event is happening tonight. As we saw in the final few minutes of last week's show, Addison and Naomi are on a helicopter with Archer, heading to Seattle to see if Derek can do anything about the parasites in his brain.
Archer's condition will be the driving force of the stories over the two hours, but there's lots of other stuff going on, too. Sam somehow ends up in Seattle, and he and Derek will reconnect for one of the first times (if not the first time) since Derek's separation from Addison. Bailey will face challenges from her colleagues about whether she's really cut out to be a pediatric surgeon. Back in Santa Monica, Violet will confront some of the challenges of motherhood head-on. And we'll learn a little more about that mystery woman Owen spotted in the hall.
Most of all, I'm looking forward to see Addison back in Seattle Grace. As much as PP has grown on me this season, I still think Grey's is where Addie belongs, and it'll be nice to see her back - even in unfortunate circumstances.