For the two good, two person case let total endowment be (X,Y) and person one's consumption be (x,y). Suppose Y>=X. Then the contract 'curve' is given by the set {(x,y):x in [0,X], y in [0,Y],x<=y<=x+Y-X}. When X=Y this reduces to a straight line across the Edgeworth Box.
For X>=Y, the contract curve is{(x,y):x in [0,X], y in [0,Y], y<=x<=y+X-Y}.
I got a sheet of paper, drew some L-shaped indifference curves, made an acetate and slid them around.