Author's note: Disclaimer: I do not own Harry Potter or Sherlock.
Prologue – The Beginning
Privet Drive an ordinary suburban street in Surry with ordinary middle class people who pretend to be a higher social standard than others was the last place you would expect for there to be any strange occurrence, the most exciting thing to happen is when a next door neighbour hosts a party to show off a new expensive work car that was actually much less than they say, but the night of Halloween in 1981 that was all going to change with the arrival of a strange man with a baby. The only person to witness the happenings was a man blending in with the shadows around him. He was here for a purpose and it was watching the strangely dressed man that he realised his job was more important than he realised.
Nothing like this man had ever been seen in Privet drive, tall, thin and very old with hair and beard long enough to tuck in his belt. Wearing a long red robe with silver stars on, a purple cloak that pooled along the ground and high-heeled, buckled boots. He had blue eyes that twinkled behind half-moon spectacles, giving off a façade of a grandfatherly type person who any and all can trust. This however was a ruse behind the twinkling eyes hidden just enough was deceit, and calculating eyes trying to figure out how to manipulate what was in front of him so he could come out on top. His name was Albus Dumbledore.
He was here to deliver the boy-who-lived to the last of his remaining family, what did it matter to him weather the boy was hated by his jealous aunt and her family knowing only disdain and hatred, who cared that it went against the wills of his parents or broke him, so long as he could manipulate the boy into being his pawn in the war none of it mattered. The brat would love him for saving him from his relatives at the age of 11 then a bit of careful manipulation and he would be a hero in the eyes of the brat. He would need a cover story as to why he is leaving the boy here. Blood wards the answer to that question and also ensures that he would have to go back each summer to keep up appearances and him downtrodden.
The hidden man watched as a cat on the wall near number 8 jumped and turned into a strict looking woman dressed in both black and emerald green and the two interacted, waiting for something to happen which was the baby being placed on the doorstep of number 4 Privet Drive. He stayed hidden until the pair had disappeared.
Slowly he walked in to the light of number 4 he had long midnight black hair, pale nearly translucent skin and a light brown green mix for eyes he was looking down at the bundle of blankets which held the sleeping baby. Gently he bends over the child and picks him up seeing the note he reads it
Mr and Mrs Dursley,
Petunia your sister was murdered during the night, along with her husband, leaving your nephew with nowhere else to go. He is a magical child and will be attending Hogwarts at the age of 11. It is up to you on what you tell him and when. I would appreciate it if you could take the boy in as he needs the protection of the blood you carry. On a side note I believe that you hold the thought that you must earn your keep, and in strong discipline also, this will not be a problem and I can guarantee that there will be no interference from the wizarding world. He will be with you until at least the age of 17. Sorry for your loss.
Regards
Albus Dumbledore
(Order of Merlin, First Class, Grand Sorc., Chf. Warlock, Supreme Mugwump, International Confed. of Wizards)
"Hmm, come on then little one, let's get you to safety" he finally speaks as he turns around and walks away to a car parked at the end of the road. It is one where the windows are tinted almost black indicating someone of importance owns the vehicle. Sliding in to the back, he states "Sherrinford's" as the car pulls away.
They arrive at the large ornate gates made of strong malleable iron painted black. The guard at the front stops them to do the normal cursory check, stopping to say hello, before waving them through.
It takes ten minutes to arrive at the house which closely resembles a giant mansion more than a house; he exits the car and walks up the stairs leading to the front door which opens just as he reaches it. Stopping only to say
"Thank you James, please alert Mr Holmes I am in urgent need of his presence"
"Of course sir, he will be there presently"
~~~~~~~~~~~ Sherlock/Harry Potter ~~~~~~~~~~~
Sherrinford Holmes entered the study, to see an old acquaintance, Victor Trent. Intrigued he took the time to sit in his chair too deduce what it was about the child he held, as this was undoubtedly what this impromptu visit was about. Taking in the moving image on the blanket (magical child) and the note clenched tightly in the hand connected to a very tense body (orphaned/abandoned), dirt on bottom of the blanket, no dirt on Victor's front or sides, small pieces of gravel under his fingertips, rumpled shirt (doorstep, bent down to pick up, unable to straighten clothes due to holding note and baby) conclusion the baby was abandoned/orphaned left on a doorstep, found by Victor who then read the note and resulted in bringing the child here.
"Sherrinford I know you have most likely figured it out by now so I shall just hand the note to you; see what you make of it"
"Hmm, little empathy towards the family most likely disdain with the way he just blurts it out, most would say 'I regret to tell you' or something along that line, words like magical, Hogwarts and the titles of the man paired with the lines you must earn your keep and strong discipline with no interference is a subtle way of saying you magic haters, here's a magical baby, raise him how you want no problem. Tries to justify it by saying he needs protection only blood can give and further antagonises them with the till he's 17 part. Conclusion the sender's an old man who is trying to uphold a façade of a grandfatherly figure whilst manipulating those around him, most likely it would have seemed as though he was saving the boy from his horrid relatives causing the abused at least verbally boy to hero worship him for being the first kind adult he would encounter, this child would most likely have had a very short and miserably life"
"Thank you, doubt I would have known all that without you. The question now however is what do we do with him now?"
"He can stay here. Clara and I will adopt him, we have Mycroft he could do with a younger brother, and I have a feeling that he needs to be prepared for the future and what better way than to grow up a Holmes besides he must be pretty important to have his life manipulated by this Albus Dumbledore"
"Really, you're going to take him in as a son? He'll need a new name"
"Pass him here, let's see him"
Victor passes the now awake Harry over to Sherrinford who look at each other intently, Harry's eyes narrowing slightly in concentration as they study each other. Slowly a smile spreads across Sherrinford's face as Harry turns away seemingly bored he states
"Sherlock, Sherlock Holmes"
Looking to the other man he continues "is there any other business you need to take care off?"
"No, no I have to be getting off; I'm late enough as it is we will sort the papers out at a later date easily enough. I'll see myself out and good luck"
"Yes, you too, see you at the usual time we'll sort legalities out then."
The last thing Victor Trent hears is Sherrinford calling his wife Clara and his now eldest son to come meet the new member of his family"
~~~~~~~~~~~ Sherlock/Harry Potter ~~~~~~~~~~~
Two weeks later Victor Trent was dredged up from the bottom of the river Thames, cause of death believed to be suicide due to being recently bankrupt and unable to face his wife and children. The case was closed and completely forgotten about, so no one but the Holmes family and help knew that young master Sherlock was adopted, and as the help loved their employers they never gave away secrets.
There was no mention of Victor Trent in the Holmes family until Sherlock's 5th birthday and that night Sherlock snuck away to the local cemetery. The morning after Sherlock was the proud new owner of a skull courtesy of Victor Trent, which he used to bounce new ideas and deductions at.