After Mary announces her pregnancy, Sherlock decides he needs to leave. He's in love with John, and it's getting too much. He knows his 'death' upset John. They almost had something then, but John had chosen Mary even after knowing her past, even after that night he and Sherlock shared...so it's time for John to focus on his wife and child, not helping Sherlock with his crime fighting games.

So without much fanfare, Sherlock sends goodbye letters to all the important people (including Mycroft) and leaves London without any real idea of where to go.

Fast forward five years and things are very different. John's marriage is over amidst much bitterness, and there is no baby Watson. He is lonely, angry, fed up and desperately bored. He misses Sherlock, he misses the crime, but has barely heard from Sherlock over the years. In desperation he contacts Mycroft only to get a chilly reception but when John refuses to leave, he gets an address in remote Scotland.

On arrival to his shock, Sherlock is there looking the same but different; calmer, more relaxed. The reason appears to be two children hiding behind him, twins apprantly, a girl and boy who look very much like Sherlock but there hints of...John too. But that would mean...that one night so long ago...is this why Sherlock left? Are these his and Sherlock's children...John

John needs answers, has questions and for the first time in forever feels like he may have hope...

mpreg is normal in this world
Bonus:
++ MyStrade are a couple who reguarly visit Sherlock and spoil the kids rotten
+++ twins are boy called Hamish and girl called Athena (just cause I can imagine Sherlock using that name!)
++++ Mycroft and Sherlock get on better but there's still rivalry