BACK FROM THE DEAD: MY APOCALYPSE LEVEL-UP SYSTEM
A low, deep sound started to rumble in the distance.
At first, I thought it was just thunder from the storm clouds. The sky outside had turned a dark, bruised gray. But the sound didn't stop, and it didn't fade away. It grew louder and louder, a steady, heavy thumping that made the metal shelves in the warehouse rattle and shake.
Thump. Thump. Thump.
"LUS," I said, my small laugh dying instantly. My hand went straight to the hilt of my plasma blade. "What is that sound?"