He promised to love her forever. But forever is finally running out. 1943: In the ruins of Blitzed London American bomber pilot Dan Rosinski encounters Stella Thorne and so begins a reluctant, impossible, unstoppable love affair in which all the odds are stacked against them; Stella is married, and the chances of Dan the war surviving are just one in five. In a time when everything is uncertain, their letters help them to hold onto the one thing of which they can be sure: their love for each other. 2011: After running from her abusive boyfriend Tia Moran stumbles on an empty house and it seems like a miracle - albeit a rather dark, damp one - a place for her to lie low for a few days. But then a letter arrives, marked Person and Urgent, and she is drawn into the story of a love that has endured for over half a century, and the search for the elusive Stella Thorne. But can uncovering the story of a past love give birth to a new one?