The storyline itself, as I have been following the news about this show since early this year, is very cool. Sarah plays twins which each has different problem in life. Gosh I dont know how to tell it beautifully so you all can be interested. But seriously, the story is very interesting. Here let me copy the storyline from cwtv.com :
The series stars Sarah Michelle Gellar as Bridget and Siobhan, Kristoffer Polaha as Henry, Ioan Gruffudd as Andrew Martin, Nestor Carbonell as Agent Victor Machado and Tara Summers as Gemma.