Complex sentence: The soldier travelling with the Doctor succumbs to his injuries, but the Doctor manages to deliver the portrait to Kinzhal: he demands to know why the Lord General is stealing treasures from the past, and how the painting causes fires.
Split into simpler sentences: The soldier travelling with the Doctor succumbs to his injuries, but the Doctor manages to deliver the portrait to Kinzhal. He demands to know why the Lord General is stealing treasures from the past, and how the painting causes fires.