King Arthur faces the collapse of his realm as he returns from his continental campaigns to confront the treachery of Mordred. The narrative follows Arthur’s internal and external struggle to preserve his kingdom against the encroaching shadow of betrayal and the inevitable decline of his golden age. Written in alliterative verse, the work captures the weight of duty and the tragic inevitability of the monarch's fall. The text serves as a reconstruction of a lost epic, framed by the scholarly efforts of Christopher Tolkien to present his father's unfinished vision.

This work is received primarily as a significant scholarly addition to the Tolkien canon, offering a rare glimpse into the author's engagement with the Matter of Britain. Critics and readers alike note the technical precision of the alliterative verse, which demonstrates a deep command of archaic poetic structures. The inclusion of Christopher Tolkien’s extensive notes provides a necessary framework for understanding the unfinished nature of the manuscript. The text is regarded as a somber, atmospheric piece that highlights the author's lifelong fascination with the intersection of myth and history.