Sherlock and John get asked to come out to a scene which is assumed to be a homicide due to domestic violence. It turns out that the dead woman is Clara, everyone except for Lestrade thinks Harry killed her in a drunken rage, and Harry was too drunk to remember what happened.

Could be Johnlock or just friends, but I'd love to see Sherlock being supportive of John and helping sort through what actually happened. Would be awesome if John and Harry got closer, too, even though they both cared about Clara and both are grieving.