Complex sentence: They are saved by their Innocence, causing the Earl, Bookman and Bookman's apprentice Lavi, who are chronicling the war, to believe one of them possesses the Innocence Heart, an Innocence that could give them victory over the Noah.
Split into simpler sentences: They are saved by their Innocence, causing the Earl, Bookman and his apprentice Lavi, who are chronicling the war, to believe one of them possesses the Innocence Heart. The Hearts is an Innocence that could give them victory over the Noah.