Fergus is invisible, but the string that Hank uses as his leash is not. Cooper, the new boy next door, sees only the string, not the dog. He also sees the large birthmark on Hankís face. Thus begins a war between the two boys, a struggle that threatens to dissolve all hope for the friendship they both crave. The climax comes when Cooper grabs the string and tries to pull it from Hankís iron grip, snapping it in two. What follows brings the boys together without threatening Fergusís existence. In fact, Fergus ends up with a friend of his very own.