Not Normal

For the prompt: "For an investigation, Sherlock and John attend a Halloween party, and since they don't want to stand out, they go in full costume. They don't coordinate their costumes and they have to meet at the party, so they don't know what the other is coming as. So they have to find the perp/solve the case AND find each other."

To find a murderer, the boys go to a Halloween costume party at a club.