Yeah, you and River were partners, but that was a long, long time ago.
Where his moment of disgrace had him demoted, you remained at Regent's Park, like nothing had even happened at all. You fell out of touch once his resentment festered to the point of it consuming him. There was a clear contrast in your places in the food chain now, and it was too much for him to handle. You had never wanted it to end that way, but sometimes, that is just how life is.
Until one day, when you end up in the center of a grisly mishap whilst on a field mission. Paranoid to the point of believing yourself to be surrounded by people you cannot trust, you stumble onto his doorstep. Smacking a weak fist in the door, you hope the blood and bruises won't be terribly noticeable from the peephole.