At some point during their acquaintance John has learnt to tell if Sherlock lied.
"Don't you see the spark of white paint on his left shoe? Of course he was there. So his sister must be the murderer."
They surrounded a particularly deformed corpse and Sherlock solved the mystery of how it came to be here, in a storage room that had been locked from the inside. Its limbs had been broken and arranged in the most unnatural way. The skull was shattered and some parts of the brain had been cut out neatly.
And Sherlock did marvellously, of course. He pointed out every detail of the deed and why the sister must be the culprit.
Sherlock looked at John and waited for praise. He got so used to it.
Except there was a certain twitch of his eyebrow. A deep line between his mouth and his almost-not-existant cheek.
He lied. He had made the whole thing up.
"Brilliant", said John.
The woman looked horribly like Sarah and at first John was sure it was her.
Thank God it wasn't.
John knelt beside the corpse on the cold, wet grass of the football field. The moonlight lit his features and made his wrinkles appear even deeper.
It also made Sherlock's skin even smoother, his eyes even brighter.
Sherlock closed his eyes as he touched his face to shove his hair away.
And suddenly there was a long, red stain on his cheek.
Of course, he had touched the corpse before.
The corpse whose heart had been torn out and stuffed into the mouth.
John looked at the stain with morbid fascination and listened to Sherlock's lies.
"Her lover's friend. Definitely. Just look at her hair! Think for one second. There are maple seeds in it. Do you see any maple trees here? We're on a football field! It was her lover's friend."
Sherlock wasn't nervous. John just knew. The way Sherlock held his head. His head with his bloodstained cheek.
"Extraordinary", said John.
When John brought Sherlock's coat to the laundry, the inside was full of white paint and in the turn-up of its collar there was a single maple seed.
John inhaled the smell of the coat - cigarettes, tea, London, Sherlock - before he gave it to the little Chinese woman who owned the laundry. As he always did.
The next time Sherlock went out without John, John followed him.
John knew that Sherlock had to know he was following him.
John also knew that Sherlock wanted him to know.
They weren't very far away from home when Sherlock entered a brothel. John didn't even try to hide and went in after a few minutes, too.
On Sherlock's lap there sat a beautiful, dark-haired woman with high cheekbones, much like Sherlock's. As soon as John entered, Sherlock let her slide off his lap, patted her bottom and followed her upstairs.
The brothel was large but it didn't seem that way. The rooms were seperated by crimson and purple curtains and there was smoke in the air which didn't smell like cigarette smoke at all. It made John feel slightly dizzy and he fought himself through the maze of net curtains until he reached the stairs.
He saw Sherlock slip through the door, not quite closing it behind him.
John does as he always does - follows Sherlock. He hurried up the stairs and peeked through the slightly open door.
Sherlock crawled over the already naked prostitute, sucking and biting her lips greedily. He was fully dressed.
Do it. Do it now. John wanted to see it. John wanted to feel it. John wanted to be part of it. Sally Donovan's words came back to his mind - because he's a psychopath - and suddenly he knew he wanted to be part of that ever since he heard these words.
So John went into the room when Sherlock took out a butcher's knife of his jacket and stabbed the already bleeding (bites and scratches everywhere) woman.
She didn't even scream. She watched Sherlock with the same morbid fascination John watched him with.
Sherlock and John got soaked in blood since the detective must have hit the outer carotid artery (John's brain supplied this information within miliseconds and it had never been so fascinating to him before). Sherlock's former white shirt was deep red and John would have to throw his beige jumper away.
The detective knelt over the dead woman and let his arms fall down at his sides. He stared at the blood-sprayed ceiling.
"Isn't it beautiful?", he asked.
"Yes, it is", whispered John.
Sherlock exhaled deeply and let the knife fall onto the floor. Then he shoved away the corpse and lay down into the pool of blood which had formed on the bed. He lay on his back, still looking up to the ceiling.
John approached him slowly and kicked the knife away before he lowered himself down next to Sherlock and curled up against him.
"I'm so glad you understand, John", whispered Sherlock hoarsly and suddenly a wet hand was in John's hair.
The blood still dripped from their faces when they finally decided to kiss. They could taste the dead woman on each other when they kissed each other's necks, bit each other's ears, claimed each other's lips.
Sherlock looked so beautiful in red, John decided.
"I know I do."