Complex sentence: Steiner's father, General Steiner, who is being tortured by the Gestapo for his ties to the German Resistance, serves as an additional incentive for the Colonel to accept the mission.
Split into simpler sentences: Steiner's father, General Steiner, is being tortured by the Gestapo for his alleged ties to the German Resistance. This serves as an additional incentive for the Colonel to accept the mission.