A massive, supernatural helmet falls from the sky, crushing the heir to the castle of Otranto and setting off a chain of dynastic crises. Manfred, the usurping lord of Otranto, attempts to secure his bloodline by forcing a marriage to the betrothed of his deceased son. He faces opposition from the rightful heirs, mysterious spectral manifestations, and the physical constraints of a castle riddled with secret passages and ancient prophecies. The narrative employs a dramatic, theatrical framework that prioritizes rapid plot progression and heightened atmospheric tension over internal psychological realism.

Readers and critics frequently identify this work as the foundational text of the Gothic genre, noting its influence on subsequent horror literature. Discussion often centers on the deliberate artificiality of the prose and the exaggerated nature of the plot, which reflects the author's interest in medieval romance tropes. While some modern readers find the pacing frantic and the character motivations simplistic, others highlight the effectiveness of the atmosphere in establishing the blueprint for later suspense narratives. The work is consistently analyzed for its role in shifting literary tastes toward the macabre and the mysterious during the eighteenth century.