On December 6, 1917, two tramp steamers, the Mont-Blanc and the Imo, collided in wartime Halifax Harbour, creating what became the largest man-made explosion of its time. More than 2000 people died, 9,000 were injured, 6,000 people were left homeless and an additional 19,000 were left without adequate shelter. In a combination of words and images (many never seen before), John Boileau delivers a breathtaking account of the magnitude of this event.