Missile Gap — Charles Stross

It's 1976 again. Abba are on the charts, the Cold War is in full swing -- and the Earth is flat. It's been flat ever since the eve of the Cuban war of 1962; and the constellations overhead are all wrong. Beyond the Boreal ocean, strange new continents loom above tropical seas, offering a new start to colonists like newly-weds Maddy and Bob, and the hope of further glory to explorers like ex-cosmonaut Yuri Gagarin: but nobody knows why they exist, and outside the circle of exploration the universe is inexplicably warped. Gregor, in Washington DC, knows but isn't talking. Colonel-General Gagarin, on a years-long mission to go where New Soviet Man has not gone before, is going to find out. And on the edge of an ancient desert, beneath the aged stars of another galaxy, Maddy is about to come face-to-face with humanity's worst fear???