It is an early spring evening in 1943 when the air-raid sirens wail out over the East End of London.
From every corner of Bethnal Green, people emerge from pubs, cinemas and houses and set off for the shelter of the tube station.
But at the entrance steps, something goes badly wrong, the crowd panics, and 173 people are crushed to death.
When an enquiry is called for, it falls to the local magistrate, Laurence Dunne, to find out what happened during those few, fatally confused minutes.
But as Dunne gathers testimony from the guilt-stricken warden of the shelter, the priest struggling to bring comfort to his congregation, and the grieving mother who has lost her youngest daughter, the picture grows ever murkier.
The more questions Dunne asks, the more difficult it becomes to disentangle truth from rumour - and to decide just how much truth the damaged community can actually bear.
It is only decades later, when the case is reopened by one of the children who survived, that the facts can finally be brought to light ...