Minerva took this in stride, noting Remus' haggard appearance. She gave him her closest approximation of a sympathetic look, a nonverbal promise that she wouldn't call on him to do anything too taxing. Poor boys, always looks thinly spread as it is. What with Potter and Black as friends...
"Mr. Lupin, Miss Evans," McGonagall said with a gesture of her wand. She took the shawl and then looked sternly at the two. "Remove your school robes and turn them orange. Should you see Mr. Harper, offer to cover him in it. Explain that Goblins can't see orange, so they wouldn't be able to see him." She looked between them again, her voice steady. "If he seems completely out of sorts, then 'herd' him in this direction. I'll have no one else hurt tonight."
With another gesture at the side corridor, she said, "You two, go that direction and cut off his route back down. Try to herd him up, so he must use this staircase."