Pilot: good, second episode: very nice, but the 3rd and this 4th episode feel somewhat 'draggy'. At the end of these episodes the story is kind of done, the characters are back where they started basically. There are no leads they can follow, so in every next episode there has to be one - if any - 'clue' for them to move on, which makes me wonder about the great plot - and conspiracy - behind everything. (Let's hope the finale won't turn out like Heroes'.)
At the end of episode 3 they had a (reservation)number, at the end of episode 4 a key. Of course, no one seems to know what to do with it, but they might stumble on to a safe or something, just like they stumbled upon that book store.
All in all it's an interesting show, mainly because of the pace. But I'd send agent Marlow on holiday or something, 'cause she is (although not surrounded by very well acting either) really unbelievable in her role as an agent. She has obviously very much trouble walking on heels and... she's just not acting very well.