Neil Oliver describes the worst ever railway accident in the UK, which happened a hundred years ago on 22 May 1915, in which three trains collided at Quintinshill near Gretna Green. One of the trains was a troop train taking soldiers to fight in World War I at the Battle of Gallipoli: many of the dead were in this train which caught fire due to escaped gas from the archaic gas lighting in the carriages. The cause of the crash was attributed to a catastrophic signalman's error, but Neil examines whether there were other contributory factors and whether there was a cover-up to prevent investigation of them, making convenient scapegoats of the signalmen.