Home for Christmas

When Mycroft Holmes informs his family he’s bringing along a friend for Christmas, the household is thrown into utter chaos: Mummy Holmes is delighted, of course and Mr. Holmes is just baffled. Sherlock, however, is determined to figure out what is his brother up to. Mycroft doesn’t do friendships, let alone relationships, so who is this mysterious Dr. John H. Watson and what’s his business with his brother?