Complex sentence: The freed prisoner's surprise is increased when he learns about Jayne's return, because he happens to be Stitch Hessian, the partner Jayne abandoned four years ago during his flight from Canton.
Split into simpler sentences: The freed prisoner's surprise is increased when he learns about Jayne's return. The man happens to be Stitch Hessian, the partner Jayne abandoned four years ago during his flight from Canton.