The Sands of Time by Sidney Sheldon
When four nuns are forced to flee their Spanish convent in 1976 to face a hostile world, they find themselves pawns in a violent struggle between the outlawed Basque underground movement and the Spanish army under the command of Colonel Ramon Acoca, who is bent on destroying them all. The author's other books include If Tomorrow Comes, Master of the Game, Rage of Angels, Bloodline and Windmill of the Gods.