Gaheris, perhaps mercifully, is out at the moment, down at the corner bar with his charcoals and his Saranac; he's well enough to do that now, and on the rare occasions that he expresses the desire, Mordred doesn't protest. If he spooks again, locking the door won't hold him.
So Mordred has the place to himself, with the newspaper spread out on the bed and a cup of instant coffee to hand. "Don't tell me," he says to the knock, "God damn it, I made sure you had the key." But he gets up, all the same, to open the door.