One possible theme could be secrecy. Since it's in the attic, perhaps their love had to be hidden. Another theme might be the power of a specific place in a relationship. The attic was where their love story took place, so it could be about how a location can shape and hold a relationship.
I'm sorry, I haven't read this story specifically. But generally, a summary might include the main characters involved in the love story set in the attic, the events that led to the development of their love, and perhaps the challenges they faced in that particular setting.
Since I don't know the specific 'love in the attic' true story, I can't say for sure who the main characters are. It could be two young people, like a boy and a girl who lived in the same house or were neighbors and discovered the attic as their special place.