Irene teases Sherlock to break his concentration/ruin his investigation. For fun. She does it by whispering dirty, sensual things into his ear about him and John having sex, because she knows that Sherlock, while he's a virgin, has a secret, guilty desire to have it with John. She also knows that Sherlock mainly fantasises about John dominating and penetrating him, so she creates a rather vivid, detailed picture of it. She gets Sherlock very aroused and then makes him have a mind-blowing orgasm just by telling him all those things, while she's smugly watching him coming undone completely.

It can be a usual verse or an omega verse with Omega!Sherlock, Alpha!John and Alpha!Irene. By the end of the whole thing, Sherlock has a large wet spot on the back and on the front of his trousers. Maybe it's quite dub-conish and Irene uses her Alpha voice to keep Sherlock from trying to leave or block her out, but otherwise is just sensual, not violent.

Pre-johnlock or unresolved johnlock is fine.