No one in. No one out.
Family can be murder . . .

It's the 1930s and a mysterious illness is spreading over Scotland. But the noble and ancient family of Inverkillen, residents of Loch Down Abbey, are much more concerned with dwindling toilet roll supplies and who will look after the children now that Nanny has regretfully (and most inconveniently) departed this life.

Then Lord Inverkillen, Earl and head of the family, is found dead in mysterious circumstances. The inspector declares it an accident but Mrs MacBain, the head housekeeper, isn't so convinced. As no one is allowed in or out because of the illness, the residents of the house - both upstairs and downstairs - are the only suspects. With the Earl's own family too busy doing what can only be described as nothing, she decides to do some digging - in between chores, of course - and in doing so uncovers a whole host of long-hidden secrets, lies and betrayals that will alter the dynamics of the household for ever.