In the spirit of the holiday and a wish for familial harmony, Irene Adler persuades her detective husband to invite his brother Mycroft to Christmas luncheon. Holmes had cut ties with his brother when he discovered the machinations Mycroft employed that drove Sherlock and Adler apart for four years. He isn't really sure this reunion is a great idea, but he can deny his wife nothing.

Of course, they can't tell the children what Mycroft is to them, as that would entail learning that their father is the celebrated detective when they know him simply as Lucca Sapori. And just when they think things may be going better than expected, ghosts of the past crop up in unexpected ways and threaten to ruin the holidays for everyone.