AU where Werewolves live among normal people and only a few, like Mycroft know about their existence. On a case, during fool moon, John gets bitten. But they don't pay any attention to it and move on. Before the next full moon John behavior starts to change and he gets aggressive, both in and out of bed. When the full moon rises, John finally turns into an wolf. He tries to kill Sherlock in his wolf form but doesn't because he can recognize Sherlock as his mate because of his smell. So instead he tries to have sex with him.

Bonus 1 - John's guilt the morning after because he attacked Sherlock.

Bonus 2 - A bit of Sherlock vs Mycroft, because Sherlock deserved to be aware of this situation.

Bonus 3 - Case fic, because l love'em. But it's not necessary.