Twelve years ago, eight friends ran an exclusive group at university: the Masquerade Murder Society. The mysteries they solved may have been grisly, and brilliantly staged, but they were always fictional—until their final Christmas Masquerade, when one of the group disappeared, never to be seen again.

Now our young, privileged cast of old university friends are summoned to the depths of Scotland for a Christmas-themed masquerade party. But all are hiding something deep below the surface that could make or break their careers.

When they arrive, each is assigned a new identity themed around the "Twelve Days of Christmas"—they become Lady Partridge or Mr. Gold, Lord Leapworth or Doctor Swan. The game begins, and it feels just like old times—until the next morning, when Lady Partridge is found hanging, dead, from a pear tree.

It quickly becomes clear that in this game the murder will be all too real, and the story is bringing long-hidden secrets to the surface. If the group hopes to win the game and survive until Christmas morning, they will need to face the truth about their history together and who they have become—and what really happened on that fateful night twelve years before.