None of the Pevensies have been in Narnia since the time they went to help Caspian. Aslan told them they would be back, but it's been years. Peter is engaged to a girl named Elizabeth, a messenger of Aslan sent to England with news for the queens and kings. She tells them of the fact the Caspian ages as they do, and has refused to marry. This makes Susan glad, until a phone call comes that same day, alerting them of a death of a dear old friend. When they go to claim their inheritance left for them, they meet a girl and end up back in a world no one but them had heard of. Narnia.

The long-lost little sister of Prince Caspian finds her way back to him. He then brings her on a quest full of dragons, seven lost lords, and last but not least - love. Heavily undergoing editing. The old (completed) version is also on my Archive of Our Own account: http://archiveofourown.org/works/8068168/chapters/18485737