Complex sentence: However, Aidan finds that a special lens he possessed was not on his person and realized he left it on Iona in the ensuing chaos, revealing that his predecessor obtained it from Crom Cruach, a pagan god with whom Brendan had a frightful encounter prior.
Split into simpler sentences: However, Aidan finds that a special lens he possessed was lost when he left Iona. Aidan reveals that his predecessor obtained it from Crom Cruach, a pagan god with whom Brendan had a frightful encounter prior.