The epic narrative opens with a scathing dedication attacking the Lake poets, particularly Southey and Wordsworth, before introducing young Don Juan in Seville. Born to a mathematically precise mother and a carefree father, Juan receives an overly sheltered, expurgated education designed to make him a moral paragon. Despite these precautions, at sixteen he becomes entangled in a passionate affair with Donna Julia, a married woman twenty-three years of age. When her older husband Alfonso discovers them in a chaotic midnight raid after Juan is forced to hide in a bedroom, a scandalous trial ensues. To quiet the gossip, Donna Inez packs her son off on a long European tour by sea.
Sailing toward Italy aboard the Trinidada, Juan encounters a brutal gale that overwhelms the vessel, forcing the crew to abandon ship in overloaded long-boats. After enduring excruciating days of starvation, dehydration, and eventual cannibalism among the desperate survivors, the boat capsizes near a rugged coast. Juan alone survives the furious surf, crawling half-dead onto the shore of a small Cycladic island. Here he is discovered and secretly nursed back to health by Haidee, the breathtakingly beautiful daughter of a wealthy local pirate chief named Lambro.
As the weeks pass while Lambro is away on a maritime expedition, Juan and Haidee fall into a deep, idyllic, and completely unreserved love, living like an ancient pastoral pair isolated from civilization. Their paradise is abruptly shattered when Lambro unexpectedly returns and discovers the illicit lovers banqueting in his hall. Refusing to surrender, Juan draws his sword and fights fiercely before being overpowered, bound in chains, and shipped away to Constantinople to be sold into slavery in the bustling Ottoman markets.
Meanwhile, the heartbreak destroys Haidee. Refusing all food and sliding into a silent, catatonic madness after witnessing Juan's bloody capture, she pines away through twelve agonizing days until she dies, carrying an unborn child to the grave. Back in the capital, Juan is purchased by Baba, the chief eunuch, on behalf of the powerful and imperious Sultana Gulbeyaz, who has caught sight of the handsome youth and instantly resolved to make him her favorite.
Kept in the sprawling labyrinth of the imperial seraglio, Juan steadfastly resists Gulbeyaz's advances out of lingering fidelity to Haidee's memory, enraging the proud queen into a furious storm of jealousy. Before the situation can resolve into tragedy, the sudden arrival of the taciturn Sultan interrupts their interview. The monarch, entirely indifferent and unobservant of the dramatic tensions surrounding him, accepts Juan simply as another pretty addition to the household, leaving our disguised hero to navigate the perilous politics of the harem.
