Destroyer of Worlds Larry Correia

The thrilling and terrifying seventy-year story—"kinetic, dramatic, and compulsively readable" (Patchen Barss)—of the physicists that deciphered the atom and created the hydrogen bomb

Only a handful of people in the world know that mankind's magic comes from a living creature, and it is a refugee from another universe. The Power showed up here in the 1850s because it was running from something. Now it is 1933, and the Power's hiding place has been discovered by a killer. It is a predator that eats magic and leaves destroyed worlds in its wake. Earth is next.