I'm spending Christmas with my flatmate this year. You would have liked him, the way you always liked simple, unassuming, honest people. He's bringing his girlfriend over; she's cooking a turkey, just like you always tried to do and never could.
I don't have a case. That'd be the best Christmas present, but it seems the Christmas spirit is infecting even the criminal classes and keeping them from transgressing the law in any but the most mundane ways.
If you were here, you'd ask why I'm not spending the day with Mycroft, even though it's obvious. It always has been—obvious in the way we look at each other, the way we speak, the way our brains repel each other. We made you upset, angry, but it was you who made us come together. You had an ideal family in your head, but you couldn't handle the reality. I frightened you, and Mycroft ran over you, just like our father did.
If you were a crime, you would be an everyday one—a smart woman, too weak to resist a man who was too much for her, who became the mother of archenemies. Easy. Boring.
Should be boring, but isn't. If it was, I wouldn't write to you on this day every year, trying to understand who you were, what secret feelings made you tear up when your sons lacerated each other with their verbal lances or what compulsion made you stay by the side of a man who treated you like a less-than-human. You should be simple, but I can never fully understand you, and you're not here for me to observe, an unsolvable case.
I don't know what to say to you, what you would have wanted to hear. I only know I want to tell you two things. I have a flatmate, and I am no longer alone.