Complex sentence: Tom is unable to convince anybody of his identity; everyone except the Earl of Hertford (Claude Rains) is convinced that he is mentally ill. When Henry VIII dies, Hertford threatens to expose Tom unless he does as he is told.
Split into simpler sentences: Tom is unable to convince anybody, except for the Earl of Hertford (Claude Rains), of his identity. Everyone else is convinced that he is mentally ill. When Henry VIII dies, Hertford threatens to expose Tom unless he does as he is told.