There was something reassuring at the fact that Johnny automatically flanked her, guns at the ready. The trust was clearly there when they could keep their backs to each other while facing any number of threats, and that was something that reminded her very much of the Johnny at home.
Right now, she was glad to have that little bit of something that she could depend on when everything else was haywire.
Mary lowered her gun for the moment, though her finger didn't move too far from the trigger, ready to regain her defensive stance at a moment's notice.
Though for now, she watched the exchange between the alien, the Doctor, and the man that had come in late and seemed... not quite human.