The central theme of The Thirteen Clocks concerns the opposition between the forces of light and warmth and the forces of dark and cold.

Although the Duke loves jewels above all things because their radiance is eternal, he seems to know intuitively that jewels are in reality cold, their radiance borrowed from mortality. The jewels of Hagga's tears of sorrow last forever. That he is drawn to Saralinda's mortal radiance—her hand is the only warm thing in Coffin Castle—shows that at the beginning of the story the Duke has not yet completely surrendered his humanity.

Ultimately, the Duke chooses death, represented by the Todal—in German Tod means death. He hopes to marry Saralinda himself when she turns twenty-one. He stops the thirteen clocks in the castle by slaying time, to make "then" eternal and prevent the arrival of...