Miracle on Baker Street (слэш)

When Sherlock grants John his miracle, when he completes the trick he began on the roof of St Bart’s, don’t you think he’ll do it at the most magical time of the year?
This is my offering for the 221B_advent community – you must go and check out all the other wonderful contributions (art as well as fic) over the course of December. Although you do have to read this first!
Huge thanks to azriona for her brilliant betaing - without her there would be commas in places no commas should be and some rather, well, strange sentences.