It was a very thick book with at least 500 pages.
The story was set in different times in Great Britain, world war II and others, but the main characters were from the future. They were from some kind of organization and they wanted to find out the events during one special night during an attack in WWII. I think it was Canterbury and it's cathedral. The final of the book was set within this Cathedral.
The main character was a male, mid 20's, 30ish. Some love was there too I think. I wish I could remember more about it!
It must have been Science Fiction for Adults oder Young Adults.
Anybody an idea? Please!