John was looking at Sherlock sitting across from him on the train, both separated by a small table, but the other didn't notice. Lost in the book over poisons he started reading when they left the station, his forehead in a frown, in deep concentration.
John was bored and the view outside the window, although beautiful and green, wouldn't keep him busy throughout the entirety of the train trip. They were on a case together, a private client, and had both brought bags with clothes enough to spend the night. Separate rooms, still. He sighed. Keeping appearances was one of Sherlock's demands; he didn't usually mind about what other people think, but keeping their affair to themselves seemed a good idea. John had agreed. And he knew, deep down, that it was the thrill of the secret and not the consequences of revealing it, that made them keep it as such.
John leaned on the seat, his eyes still on Sherlock, the empty carriage, the two of them alone. The door between carriages was open though, and John could see other people reading books and listening to music, some writing, some even sleeping. A wild thought crossed his mind and he smiled to himself. Sherlock didn't notice it. But he felt. As John undid his shoe and his foot slid between Sherlock's thighs, he froze in place. Still looking at the book, still staring at the pages, but his eyes gazing at words he would not see now. He raised his eyes from the book at last and looked at John, who was still grinning. With Sherlock's attention completely on him now, he moved his right foot, slowly. The jeans were rough but he could feel Sherlock, he could feel the effect he was having on him. They had never held hands on public locations and their kisses were stolen on dark alleys and empty streets. This was new and exciting, and made him feel braver, daring.
Sherlock placed the book on the table, still open, but he didn't say a word and John took this as an incentive. He continued. Rubbing his foot up and down Sherlock's crotch, he felt the bulge underneath his feet. He continued slowly, but rhythmically. Sherlock half-opened his mouth and John saw him exhale, trying to even his own breath to no avail.
Sherlock eyes stared into his and the detective finally leaned his head back and clutched at the seat, his hands closed in a fist. John was enjoying it almost as much as Sherlock was and he started to move his foot in circles, up and down.
"Don't stop."
The words were so low that John wasn't even sure he had heard them or just imagined. But he didn't stop either way. Sherlock was now looking right into his eyes again and John wished he could just rip off his jeans right there. But he couldn't. He felt Sherlock's hand touching his foot and as Sherlock rolled his eyes and bit his lower lip, trying to suffocate a moan, John felt the wetness on the sole of his foot and he laughed. Sherlock had come, with a footjob and on a public place. So much for the consulting detective who had everything under control.
John allowed Sherlock to get back to his senses and then he put his shoe back on, relishing on the expression on the detective's face, enjoying the power he had. Sherlock got up, keeping his things, adjusting the bag so that it would cover him and all the evidence of what had really happened on that empty carriage.
"It's our stop." He said, pointing out, as people moved away from the train. John got up, his own erection making it hard to walk. He imitated Sherlock and used his bag as cover and they walked out of the train together.
The crowd was rushed, looking for their destination on the big boards at the central station and John focused on anything else but the moment they had shared, trying now to even the beating of his heart. He felt Sherlock's hand tugging at his sleeve and, before he could even acknowledge it, he was being pulled into the public bathroom.
Sherlock waited for the stranger by the sink to finish washing his hands and leave, and pushed John into one of the stalls, putting the lid of the toilet down, placing the bags on top of it. He pushed John into the wall and didn't waste any time. He kneeled down and unzipped John's trousers, with precise but soft movements. John was still half-hard and as Sherlock's tongue licked him eagerly, it was his time to lean back against the wall and enjoy the moment.
More people were walking in and out of the station's bathroom and John grabbed Sherlock's hair, trying not to scream. Sherlock was skilled and his tongue was wet and the world was spinning. The consulting detective didn't pull away when he came and the sensation was exhilarating. He hoped his low moans had been muffled by the day to day sounds of the station, because he could not be sure to had been able to restrain them enough.
Sherlock cleaned himself and leaned against John, bodies close, separated by sweaty clothes but satisfied. He brushed John's hair with his fingers, looking down at the doctor. He kissed him gently, his whole body sensitive to the touch.
"I didn't think you had it in you, Dr. Watson." He said, playful.
"Is that a challenge?" John asked.
The other didn't speak, but he nodded, smiling.
"Accepted." John whispered and he reached out for him again.
The taxi ride from the station to the hotel was a long one. But as the door of the room closed behind them, and the bags were thrown to the floor and ripped clothes fell to the ground, they knew the challenge was never meant to see an end.