You are a wizard busy all day with protecting sheep. There is an evil giant who is targeting innocent sheep: he throws stones at them but you are going to make sure that the stones don't reach the sheep. This you do by drawing lines, that convert into beams that will block the stones. The beams are there only temporary and the giants keeps throwing stones, who keep on bouncing so you have to keep on drawing lines. Try to keep your sheep herd complete as long as possible!
Keep the left mouse button presses down when you draw the lines.