Friel had originally intended on writing a play set in Derry after moving to the city in 1968, and changed its contents after being present at the Bloody Sunday massacre in January 1972.

In Derry, Northern Ireland in 1970, the play interweaves the present (a tribunal into the deaths of three civil rights protestors at the hands of the British security forces and the reaction of the city's populace to the killings) and the past (the final hours of the three protestors who have mistakenly found themselves in the Mayor of Derry's parlour in the Guildhall after attending a Northern Ireland Civil Rights Association march).

The protestors, who stumbled into the parlour after the march was targeted with tear gas by the security forces, discuss their personal stories as they attempt to wait out the violence in order to go home.

Their presence in the building is mistakenly interpreted as an occupation, and the three eventually attempt to escape from the Guildhall, but are shot and killed by three soldiers after surrendering.

The tribunal concludes with the judge finding the soldiers innocent of any criminal charges, based on fictional eyewitness accounts which stated that Lily and Michael were armed.