In 1967, witnesses watched glowing objects descend toward the water off Nova Scotia. The official search found almost nothing. Decades later, former military personnel began telling a much stranger story.

On a cold October night in 1967, something lit up the sky over Shag Harbour, a small fishing community on the southern edge of Nova Scotia. The witnesses were ordinary people: teenagers, fishermen, residents looking out toward the Atlantic. What they described was not subtle. Orange lights appeared over the horizon, moved rapidly through the sky, then seemed to descend toward the ocean. Some believed they had just watched an aircraft go down. That assumption mattered, because it transformed a...