This was stupid.
Sherlock looked out on the lake, glared at John, and sat in silent defeat. It wasn't his fault he'd nearly drowned four days earlier chasing after a suspicious swimmer (who turned out to be just some swimmer). Only a few yards in, Sherlock's mind and body suddenly reminded him that he could not and would not swim, and he began going under.
John tried to run in and lead the rescue mission, but—to Sherlock's dismay—Anderson was an excellent swimmer and beat him to it. The detective won't admit it, but he carefully considered beating Anderson off and fending for himself. But had he survived (on the off chance), the good doctor would have finished him off.
Really, if he admitted it, John didn't want to be standing on a hot lake beach with a moody detective, either. Sherlock probably didn't need to learn the trick, but there was always a chance that a criminal would plunge into the waters. Both men knew that, possessing the ability or not, Sherlock would follow. Learning was for the best.
Sherlock's shirt stayed on after he'd taken it off and John made some crack about his porcelain skin cracking in the sun. The man still looked comical; his trunks were a good two sizes too big and displayed four bright-orange fish chasing each other in a dark blue ocean (they were the cheapest ones he could find). His sunglasses, then, didn't look too bad, but raccoon eyes were already forming.
"I don't see why you're shy about getting in now," John said with no shortness of sass. "You weren't hesitant a few days ago."
"Adrenaline, John. It's a powerful thing. This, this is preposterous."
"Hush. Now go on."
"Well aren't you going to teach me?" Sherlock asked, crinkling his nose.
"My father taught me by throwing me overboard. I could get a boat, if you'd like."
"Unnecessary." Sherlock took a deep breath and stepped in the water. Cold, grimy, opaque liquid. What had he been thinking the other day? He was sure that the swimmer was a tie to the Albanian trafficking ring; something in his stomach just told him so. No deduction. No reason. Something, something inside him made him stop the cab, abandon John, run a good fourth mile, and plunge into the lake. It took mere seconds for him to panic at his mistake.
Other than four days ago, he'd been in the water twice. The last time was right after the pool incident with Moriarty. Sherlock returned to the pool to see if he could extract any evidence. He found nothing and, lost in his mind palace, ended up walking right off the ledge and into the chlorine-infested goo. He scrambled out, soaked, and stayed out of 221B until he was completely calm and dry.
The first time was when he was nineteen, alone, addicted, and inbred with a terrible fear of drowning. It would be the perfect way to…well. Had Mycroft not shown up, Sherlock wouldn't be here.
John, now impatient, walked up to the shore. "Don't think I won't throw you in. We have things to do, Sherlock, and I'm not going to wait all—" John stopped as he saw two tears hiding in Sherlock's eyes.
He walked away, grabbed the orange shock blanket—he'd kept it, of course, ever since the pill suicide case—and put it around the detective's shoulders. It was the only blanket he'd ever use without a fight. "Okay. We can try later. Come on." He led his friend away and sat him on the sand. "It's fine. We're done for the day."
To this day, the good doctor thinks Sherlock is just really, really stubborn and somewhat afraid of water. Sherlock plans on telling him the truth later. Maybe. At least, if he tells anyone, it'll be John.