Complex sentence: The entire first half of the film leads up to the Night of the Long Knives, in which Karl is arrested and sent to Dachau Concentration Camp and it is up to Helmut to get him out.
Split into simpler sentences: The entire first half of the film leads up to the Night of the Long Knives. During this time Karl is arrested and sent to Dachau Concentration Camp and it is up to Helmut to get him out.