Valley of the Squinting Windows is a classic Irish novel set in central Ireland c. 1914-16 in Garradrimna is a tiny village where everyone is interested in everyone else's business. Twenty years before the events of the book, Nan Byrne has a relationship with a local man, Henry Shannon, hoping to marry him for his wealth.

She falls pregnant but Henry refuses to marry her. After a miscarriage, the baby is buried at the bottom of the garden. Henry marries another woman and later dies, while Nan herself emigrates to England and marries Ned Brennan.

They later move back to Garradrimna, where the villagers rejoice in telling Ned about his wife's past. Ned is brought low by the humiliation of his wife's past promiscuity. He drinks and makes a little as a labourer, whereas Nan works every day at sewing to support their only child, John, studying in England to become a Catholic priest.

However, she becomes as cruel, petty, and jealous as the rest of Garradrimna, conniving with the postmistress to sabotage Myles Shannon's chance at romance with an English girl, to get revenge on the Shannon family for rejecting her. Her son John returns to Garradrimna for a holiday, where he befriends Ulick Shannon (son of Henry) and falls for Rebecca Kerr, a schoolteacher. Ulick and Rebecca have a relationship however, and when Rebecca becomes pregnant she is disgraced and expelled from the village.

Ulick abandons her and John murders him, weighing the body with lead and hiding it in the lake. Rebecca leaves for Dublin and an uncertain future. An old gossip informs Nan and John that she witnessed the night Nan gave birth to Henry's child - in reality, the child was born alive and was given to Henry and his wife - who they raised as their son, Ulick Shannon.