About to get married, Mirabelle and her fiancé retired Superintendent Alan McGregor are torn about where they will settle but when a once-in-a-lifetime opportunity comes up to buy a secluded house on the banks of the Firth of Forth, they submit to getting permission from the local landlord. But that permission comes at a price and when a nun dies in mysterious circumstances at the Little Sisters of Gethsemane Convent nearby they are drafted to uncover what happened.