Ferry disaster on Grey's

From TV Guide...
Episode Detail: Walk on Water - Grey's Anatomy
The beginning of a three-part story arc in which a ferryboat disaster poses stern challenges to the interns.

Not much there to go on, but I still can't wait to get home tonight to watch. :)
I heard the city of Seatle was very concerned about this one and any suggestions that their ferry boats weren't safe.

Totally not related to tonight's show... I heard DENNY could be making a reappearance in an upcoming episode. Not sure if it's his evil twin or just a dream!