It is 1895, England has banned Opium. Sherlock is 20, gay and secretly in love with his friend James, both use a lot of opium and alcohol. They share a house in London.
Mycroft has been selected to establish a special unit within London Police to investigate threats to the crown originating within England. Mycroft has also been made Sherlock's trustee overseeing his allowance since the death of their parents.
James gets in debt to a criminal. James tries to middle man some opium as a way of paying off his debt. He enlists the help of Sherlock who is at first reluctant, but sees it as a way of humiliate his brother.
Mycroft is getting reports about this activity, initially not knowing Sherlock is involved. When he learns he tries to steer his brother from harms way. This only increases the rivalry. James gets more involved and this increases the danger for both Sherlock and James. They identify an illegitimate daughter of a politician and use it to help import some opium. This goes wrong and it appears that a third party is hunting down all involved to take over the opium trader. Their local opium den is destroyed by three masked men who murder the shop owner. These men also kill others as they make their claim.
Sherlock give some information to Mycroft in a hope that he will act and unwittingly assist Sherlock.
Sherlock and James team up with the daughter (Rose) to try and escape the violence that is pursuing them without going to jail in the process.
Rose is as smart as Sherlock. He is loves her in a non-romantic way. She impresses him at every turn. While Rose is out getting information. She discovers a warehouse on the doc at the same time as James. They are becoming jealous of each other. This appears to be the place the opium is going to be dropped.
James and Rose are abducted by the criminal James owed money. They are taken to the drug buy. When they arrive it is a trap, guns fire and people die.
Sherlock arrives to find Rose wounded and dying. It appears that have taken James. Sherlock give chase. He hears bodies being thrown in the water. He sees one of the hooded men and gives chase. The hooded man is headed for a small boat. Sherlock shoots at him. Forcing him to change direction. There is a chase that end on the bridge leading down to Parliament and the tower housing Big Ben.
Sherlock gets the person to stop. They remove their hood. It is JAMES.
Sherlock is devastated. Mycroft appears and tries to talk Sherlock into dropping the gun. He shots. The bullet nicks James' face. James flees. Sherlock is dragged to the ground by Police. Mycroft gets them to let him go. Mycroft give him an alibi "This is Sherlock. He has been work for me as a Consulting Detective".