At 7.14 a.m. on 30 June 1908 a huge fireball exploded in the Siberian sky. A thousand times the force of the Hiroshima bomb, it flattened an area of remote Tunguska forest bigger than Greater London, forming a mushroom cloud that almost reached into space. Six hundred kilometres away, the Trans-Siberian Express rattled wildly on its newly built tracks. Tremors registered in distant St Petersburg, and the unusually bright night skies seen across England over the next few nights prompted letters to The Times. A century on, and no-one knows for sure what really happened. Suspects range from comets or mini black holes into the realms of sci-fi and conspiracy: a laser beam fired by extra-terrestrials or an early nuclear experiment. Surendra Verma tells the incredible story of the Fireball and of the scientists and charlatans alike who have been seduced by it.