For Rosie's first real Christmas, she has requested something special.
Sherlock puts everyone onto the case and he and John realise that, were they to ask for something special for Christmas they'd already have it - right under their noses.
- Part 1 of The Gambit
As they have returned home to Baker Street after having spent Christmas at the Holmes', Sherlock Holmes, John Watson and their daughter meet with Harry Watson and her fiancée Clara who are in need of some help.
- Part 2 of The Gambit