Go to the Rooftop Battle level. When the clowns chase Mary, you will go up to the rooftops. Grapple hook up to her roof and beat up the white clown. Go up to the next roof, where you are on a little balcony. Jump across, then go in to see a thug run across a hall with the girl. Follow and he will jump off the roof. Follow, look down, and drop to lowest edge. Walk along to left until at the corner the grapple icon appears Grapple over, go in the door and pick up Envelope A.