Trespasses tells the story of Cushla Lavery, a 24-year-old primary school teacher living on the outskirts of Belfast in 1975. She works occasional shifts in her family’s pub, managed by her brother and often stepping in for her alcoholic mother Gina. The violence and terror of Troubles-era Northern Ireland is a constant backdrop, and forms the basis of her young pupils’ life experience and their everyday vocabulary. Cushla’s town is relatively mixed compared to some more religiously segregated areas, and while her family are Catholic, their bar is frequently by a friendly mix of Catholic and Protestant drinkers, who by and large rub along well together. It’s at the bar that she meets the much older Protestant barrister Michael Agnew, with whom she begins a secret affair. In parallel, she begins to provide additional care to one of her young pupils, Davy McKeown, whose father has been maimed in an attack. Those two dominant strands of her life eventually intertwine with catastrophic consequences.

The Marriage Portrait is a heavily fictionalised version of the short life of Lucrezia de' Medici, a sixteenth century member of the renowned aristocratic House of Medici in Italy. As the novel's introductory note explains, she was betrothed to Alfonso II, Duke of Ferrara at very young age, and died fairly soon after their marriage, with persistant (though unproven) rumours alleging that she was poisoned. O'Farrell's interest in the subject was spurred on by seeing a surviving portrait of Lucrezia, attributed to Bronzino, and Robert Browning's poem My Last Duchess, which covers the same subject matter.