Complex sentence: O'Flaherty is assisted in this enterprise by others, including locals, clergy and the diplomatic corp. The Nazi's attempts to destroy the group, but Kappler is frustrated by O'Flaherty's successes, due to his cleverness: disguises, and stressing the Vatican's neutrality.
Split into simpler sentences: O'Flaherty is assisted in this enterprise by others, including locals, clergy and the diplomatic corps. The Nazis attempts to destroy the group, but Kappler is frustrated by O'Flaherty's successes, due to his cleverness: disguises, and stressing the Vatican's neutrality.