A Colder War by Charles Stross

An alternate-history Cold War thriller in which mid-20th-century scientists stumble onto forbidden, extradimensional forces and technologies; instead of being hidden, these discoveries are militarized by competing superpowers, triggering a secret arms race of occult science, bureaucratic intrigue and escalating escalation that culminates in a catastrophic confrontation with incomprehensible cosmic entities that shatters old certainties and redraws the map of geopolitics.