Complex sentence: Duke Gerald, Peter's brother, refuses to tell about where he had been in the night, in order to protect Mrs. Grimethorpe; he risks being hanged for a murder he did not commit rather than betray her.
Split into simpler sentences: Duke Gerald, Peter's brother, refuses to tell about where he had been in the night, in order to protect Mrs. Grimethorpe. He risks being hanged for a murder he did not commit rather than betray her.