What are some examples of books where an important event is not revealed to the reader?

What are some example of books where an important event is left out of the book and only indirectly described, or leaving the event as an open mystery after the end of the book?

To be very precise, what I am looking for is when a book revolves around a certain event, and it only reveals small parts of the event throughout the novel, possibly out of order, leaving the reader to piece together the full description of the events in the book. I am not expecting there to be any books that completely fit this description.

I almost want to describe it as a MacGuffin, but that is more of a seemingly important object, not an event.