The story opens in Frederick's youth. His father, Frederick William, was a rough, burly man, fond of outdoor sport, a hearty eater and a heavy drinker. Because his son was frail and delicate and more interested in intellectual matters than in sport and hearty living, Frederick William hated him. He forced Frederick to drink and smoke, and on one occasion when the boy defied him on the subject of a favorite flute, attempted to strangle his son with a window-cord. From these joyless days we shift to the tragic death of the old king, hastened by the receipt of an insulting message from the Austrian emperor. With his dying breath, Frederick William besought his son to avenge him. Frederick heaped coals of fire on the head of his dead father by laying Austria waste in the terrible Seven Years' War. Amalie, Frederick's sister, fell in love with Baron Trenck at first sight, and their love that started in the palace garden at Sans Souci lasted all their lives. But if it started with roses and moonlight, it ended with ashes and rue, for years later Trenck was imprisoned by Frederick on a charge of high treason. Amalie pleaded for her lover, but in vain. The king was obdurate. "Even as you have taken from me the only thing I loved," cried the poor princess, "so may God deal with you, brother." Frederick did not have long to wait for the fulfillment of his sister's prayer. The discovery that Voltaire, the great French philosopher, whom the king had honored with his friendship, was playing traitor, nearly broke Frederick's heart. A tremendously dramatic scene shows the king reviewing his army for the last time, and raising his trembling hand to the salute as the flag passes. Last of all, the great king, lonely for all his greatness, is talking to two little peasant children in the grounds before his palace.
—Moving Picture World synopsis