The death of Conrad in Horace Walpole's The Castle of Otranto is the event that launches the entire action of the novel. Occurring in the very first chapter, this sudden and supernatural death is charged with significance, setting the Gothic tone, driving the plot and pointing toward the working out of an ancient prophecy.
The manner of the death. Conrad, the sickly and unpromising only son of Prince Manfred, is due to marry the princess Isabella on his birthday. Instead, on the wedding morning he is found crushed to death beneath an enormous helmet that has fallen mysteriously in the courtyard. The grotesque, inexplicable nature of the death immediately establishes the supernatural, terror-filled atmosphere of the Gothic novel.
Fulfilment of prophecy. The death recalls the ancient prediction that the castle and lordship of Otranto should pass from the present family whenever the real owner should be grown too large to inhabit it. The gigantic helmet, and the giant limbs that later appear, mark the beginning of that prophecy's fulfilment. Conrad's death is thus the first sign that Manfred's usurping line is doomed.
Trigger of Manfred's desperate scheme. With his only male heir dead, Manfred fears the loss of his succession. In panic he resolves to divorce his virtuous wife Hippolita and to marry Isabella himself in order to father a new heir. This monstrous plan drives the whole plot: Isabella's flight, the pursuit, and the train of terrors that follow all spring from Conrad's death.
Thematic significance. The death introduces the novel's central concerns of usurpation, guilt and retribution. It signals that the sins by which Manfred's family seized Otranto will be punished, and that fate and the supernatural govern human affairs.
In conclusion, Conrad's death is highly significant. It opens the novel with Gothic horror, sets the prophecy in motion, provokes Manfred's ruinous designs, and announces the themes of doom and just retribution that shape the entire story.