John felt the black, icy water swallow him up. As soon as he hit the water, he heard a loud explosion, and the blast pushed him a little bit away. He sunk, feeling the water pressure become heavier and heavier. He opened his eyes, getting used to the water stinging it. He looked in all directions and eventually found the one that was lightest. The one that was the surface.
He swam to the top quickly, fighting the currants, taking deep, delicious breaths as he broke surface. He looked over at Tower Bridge, which was now a fiery pile of blocks and rubble.
John looked around for Sherlock. He was nowhere to be seen. John's heart raced as he dove back under, kicking off his shoes so less would drag him down. He span and glanced in all directions, hoping to find a glimpse of something.
What if he couldn't find Sherlock? Of course he didn't have Moriarty's timer, but he had the timer of how long one could last without breathing. This isn't what John wanted! It was either save them both or both of them die. Having one live and the other die was simply not an option. Especially having Sherlock die and John live. John couldn't let him do that. Not again.
He went to the surface and grabbed another lungful of air. As he went back down, he saw something. A taller human wearing a scarf and coat. He swam to Sherlock, fighting with all his might to fight the currants. Eventually, he grabbed the poor man's hand, and tried to drag him up. He didn't budge. He studied the man and noticed that his scarf was latched onto a log.
John could have screamed, if he hadn't been underwater. He just wanted his best friend. You've had your fun, universe, just let them live. He wrestled with the scarf for a long moment, his lungs bursting from lack of air. John finally reached around the man's neck and tore the scarf, freeing Sherlock.
He grabbed the still-unconscious man and dragged him to the surface, taking in much more air. The currents were much harder to fight, now that he was swimming for two. He ignored the murky water that kept splashing over his head, and did his best to avoid all boats. He eventually pulled Sherlock to the shore, and John shakily pulled himself onto his hands and knees. He vomited out the foul water that he had swallowed.
By now, the police had gotten to the bridge. A few of the police, including Lestrade, ran to the two wet men.
"John! What the hell-" Lestrade began, stopping when John put up his hand.
"Water. Need water," John rasped, and one of the cops took off to find water. John crawled back over to Sherlock, his mouth still tasting like vomit. He put his ear to Sherlock's heart. It was still beating, barely. Sherlock was making sick, choking noises.
The policeman returned to John and tossed him the water. John took a few gulps, rinsing out the vomit and river water.
"Go and get the medics," John instructed, and Lestrade went to do so. John crouched over Sherlock and tipped the unconscious man's head back, opened his mouth, pinched his nose, and forced air from his own lungs into Sherlock's. He pressed down on Sherlock's stomach a few times, and with another choke, Sherlock spat globs of water out of his mouth. John did it again, and got the same result. By this time, medics were there. They helped John away and put Sherlock on a stretcher, pulling John back when John tried to follow.
"I need to go with him! He's my friend!" John repeated over and over.
"Sir, we have to take you to the hospital, too," someone said. He felt a fleece blanket drape over him. A shock blanket.
"No! I'm fine! I need Sherlock! I didn't spend all this time finding him just to have him taken away again! I need him. He needs me."
"Sir, your head has a large gash in it, you swallowed too much water, and-"
"Please! He's… Please!" John pleaded. John was crying at this point. "He needs me! I fucking need him!"
"If you would just cooper-"
John felt his legs go out from under him, heard a scream, and he blacked out.