Disclaimer: Jack Harkness and Mycroft Holmes are borrowed only.
A/N: This is actually what started all this - I wrote this snippet down, then started thinking how it could have come about...
8. Christmas Day, 2002
Then come Sherlock's drugs and the days blur into a maelstrom of worry and anger and yet more worry, watching his baby brother self-destruct and feeling helpless, until Christmas is the last thing on his mind and Jack Harkness' visits even further than that.
So he doesn't even notice that the pattern gets broken.
He spends the days around the pointless holiday in the waiting room of a clinic, living on awful coffee and tasteless snacks and little else, knowing Sherlock is going through a hell of his own making – he can hear the screams, for a while, and the puking – and he can't help – might do more harm than good – but he can't leave either, and the sad-looking sparute tree that appears in a corner in a miser attempt at bringing some cheer in a place devoid of it barely registers in his consciousness.
Harkness finds him anyway, on what is most likely Christmas Day, though for the first time in his life, Mycroft has lost track of the exact date.
The never-changing man sits next to him silently, for hours, none of his usual flirting jokes and infuriatingly tantalizing tidbits of knowledge, just a warm, comforting presence by his side, not quite touching – Mycroft's grateful for it, he isn't sure he could bear it with composure – but not leaving him to his nowadays-usual bleak thoughts.
Mycroft won't admit it of course, but he's surprised. He has never thought of Jack Harkness as a source of comfort, not even in the rare moments of sex-induced fondness; but as it turns out… he is rather good at it.
And Mycroft, uncharachteristically, is genuinely grateful.
When he rises to leave, Jack hands him a vial of murky yellow liquid. "To help with rehab," is the only thing he says. "Merry Christmas."
(Mycroft's overtired brain still works excellently – he has read a classified report on this serum, he remembers: the substance will not help with the addiction but if his brother can kick that, this will ensure the aftereffect are minimised through cellular regeneration – how is he ever going to repay the man for this?)
"...Merry Christmas," he manages in a whisper – but the man is already gone.