At the heart of the narrative within The Hollow Hills lies a profound contemplation of humanity’s autonomy and the acceptance of one’s inevitable path — the central theme weaving through the entire saga of Merlin and Arthur. In The Crystal Cave, Merlin stands at a crossroads, confronted with the choice between the essence of manhood and the allure of power. Opting for power, he dedicates his existence to guiding Arthur, his other self, towards mastering dominion over the land.

In The Hollow Hills, Arthur strides forward to embrace his ordained role as the warrior king, yet inadvertently sows the seeds of his own downfall. His fateful union with his half-sister Morgause leads to the birth of Mordred. Within The Wicked Day (1983), Mordred, aware of the grim prophecy foretelling his role in his father's demise, harbors love and loyalty towards Arthur. Yet, he finds himself ensnared by the seductive grip of power and the relentless force of destiny, ultimately fulfilling the prophecy.

Through these intricate tales, Stewart seems to suggest that while humanity possesses the gift of free will, it is burdened with immense responsibility. This freedom invariably aligns with the overarching design of a greater force, whether it be God, destiny, or fate itself.