Please Help Me Name This Book

Takes place in East Berlin around 1948. A father and daughter try to escape through tunnels to West Berlin.  I think her father makes it through but she doesn’t.  I remember it was a set up, daughter hides when authorities show up.  Next day she goes to work at a East German military base.  

Her boss is a Colonel and is attracted to her.  They start an affair.  Long story made short, the colonel has been sneaking people out of East Berlin.  End of book they marry and move somewhere in Eastern Europe where no one knows them.

Thank you.

Mary