Mycroft gives Sherlock the apparently simple task of solving a puzzle box containing a stolen microchip. It isn't simple.

“I’m not his date,” John snaps, for what must be the fucking umpteenth time in the fucking week.

"This is why you didn't tell me, isn't it," John said.

“A few weeks ago I would have thought you were impossible,” Sherlock begins, walking into the kitchen in his blue robe, and John – not quite catching on – wants to scoff and argue, No, actually, you are impossible, but then Sherlock continues: “But now I’d say you are improbable.” John thinks this might be flattering, if he could wrap his head around it, but he can’t – Sherlock is standing near, steaming his sun-baked-clean-sand smell, like the beach after rain, an alive smell, an other smell. It’s intoxicating, and John has been studiously avoiding it, but he can’t shift away now it’s so near. Now Sherlock’s so near. And then Sherlock ruins the probable-loveliness of his words and the definite-beauty of his presence by saying: “And by ‘improbable’ I mean ‘not yet scientifically acknowledged.’”

On any given day, Sherlock might come out of the bathroom smelling like an Alpha on the hunt (Alpha #8) or an Omega in heat (Omega #9), a Beta brooding (Beta #3), or like no gender at all. The last one was his actual scent, which wasn't so much scentless as confusing. At least in an adult. If Sherlock and John were the sort of people to read Mills and Boon novels, they could have said that what occurred was because destiny intervened and set two destined lovers in their one true pairings' path. It was the lasagna.

They'd never talked about sex in the year they'd known each other. Well, that wasn't quite correct: Sherlock had never said a word about sex; John had bemoaned his personal dearth of it on many occasions.

John and Sherlock have something in common of which they are both unaware. They've both been holding back from starting a relationship with the other because of the one aspect of their lives they are *sure* they cannot share. Serial Killer AU.