The Foreshadowing Of You And Me Sherlock x reader

What happens when Sherlock's long time wife comes back and meets John Watson and starts solving crimes with them? What happens when the reader is the worlds greatest detective? unknown to John until they need her help, she was in the fbi and was able to solve all the cases nobody else could. What happens when they learn the truth of where she comes from? What happens when an old enemy threatens to expose (y/n) will Sherlock stop the person or will (y/n)s live be exposed to the public? They are in for the ride of their lifes