Complex sentence: Hitler was unaware that his own envoy, Admiral Wilhelm Canaris, head of the "Abwehr", was running a secret resistance movement and liaising closely with Franco by specifying particular terms that Hitler was certain to refuse.
Split into simpler sentences: Hitler was unaware that his own envoy, Admiral Wilhelm Canaris, head of the "Abwehr", was running a secret resistance movement. Canaris liaised closely with Franco by specifying particular terms that Hitler was certain to refuse.