One minute Desmond was turning the key on the island...the next minute he's with his girlfriend and everything's wonderful?:confused:

.....Then he changes the outcome of events while in the past which thrusts him back into the future that was predestined for him.

It looks like the key actually has the power to return someone to the past + an additional 24 hours to correct wrong things. Remember when Des is in the pub and says "I'm one day ahead" or something like that?

Anyway, I get the feeling Des has realized the key has the power to correct things. What I don't understand is why Des is trying to save Charlie?

This is making me think back to the "sky turning purple" comment from Tom. And when you put that together with Lost Time, maybe from the time the key was turned they coudn't go back to the present. And going back to the past would mess up the whole space time continum thing and mess with the fate of humanity?