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.

Milkman is told in the distinctive voice of an unnamed 18-year-old "middle sister" trying to go about her life in an unnamed city in peak-Troubles Northern Ireland. She is stalked and harrassed by a 41-year-old paramilitary officer known only as "Milkman". False rumours spread that she is in a relationship with this character, affecting her relationship with her mother, the wider community, and her "maybe-boyfriend".