Assassin just waits for Shifter's word but in the mean time he will start looking and whatever might be coming from the outside.
Once the shifter is down he will find a quiet place and shift back to man form then look about to see if he can see the front entrance. He will stay in the darker areas if possible to remain out of sight.
I don't know if you need our actions yet but Assassin will continue to wait outside until he knows something from Shifter.