In the Days of the Comet - H. G. Wells

William ("Willie") is a student living in the British town of Clayton. As a Socialist, he tries to move power from the upper class to the working class. Interestingly, in a fictitious confrontation Britain declares war on Germany. Willie falls in love with Nettie, but when she elopes with an upper-class man, Willie resolves to kill them both. Throughout the novel there is present in the sky a large comet which gives off a green glow. As Willie prepares to shoot the lovers, two battleships appear and begin shelling the coast, causing Willie to nearly lose his targets. As the comet enters the atmosphere, it gives off a green gas which envelopes everyone including Willie, who falls asleep. Willie wakes up a changed man. He is able to reason so clearly that he realizes the foolishness of his plan for revenge. Other people have changed too. Our hero marvels at how humankind has risen to new levels of vision and understanding. (Summary from Wikipedia)