The Body In The Attic by Katherine Hall Page (2005, Paperback, Reprint)

Caterer Faith Fairchild and family are living in one of historic Cambridge, Massachusetts', venerable Brattle Street houses while the Reverend Tom teaches a course at the Harvard Divinity School and does some soul searching -- is his Aleford parish his true calling? One night in downtown Boston, Faith is startled by a face from her past. It's Richard Morgan, a former boyfriend from her life as a single woman in Manhattan. Their heady, whirlwind affair in the waning days of the self-indulgent 1980s ended abruptly. Now he's back, as exciting as ever.

Then something occurs that turns a pleasant sabbatical into a nightmare -- Faith discovers a diary, written in 1946 and hidden in the attic, that reveals an unspeakable horror. Suddenly dark secrets seem to permeate every room. And with Richard guarding strange secrets of his own, Faith is soon caught up in solving more than one troubling mystery ... with a murderer lurking a little too close to home.