After stopping, the elevator doors opened, but no one came out. The hallway was empty, not even a sound of footsteps. Then, from behind the sealed door on the 64th floor, came a soft, "Huh?" as if surprised to find a door there. The lock on the 64th-floor door slowly started turning. It was as if a hand was gently and carefully using a tool to pick the lock. The hand picking the lock moved patiently and slowly, like it didn't want to get caught. But the door didn't open. Just then, Caroline rushed over to the door, unlocked it, and stepped out, getting ready to head downstairs. Nelson had just developed a new drug! It wasn't finished yet, but it could be used on some critically ill patients. She planned to send a batch down. But when she opened the door to head to the elevator, she suddenly felt a chill down her spine. She quickly turned toward the door. No one was there, completely empty. Caroline wondered if wearing the protective suit was messing with her vision and instincts, making her see things. Frowning, she locked the door before taking the elevator downstairs. She didn't know that the moment she stepped out, someone invisible had slipped onto the 64th floor. The invisible figure kept moving up and had already reached the 66th floor. Raven, who had been lying on the floor, suddenly stood up and looked toward the door. Seeing Raven stand, Jet tilted his head and asked, "What's wrong?" He also perked up, listening intently for any sound outside. In Tyler's room, Snow had been chewing on a toy, but suddenly straightened her back. Silver got alerted too, staring at the door.All four of these highly sensitive, mutated creatures sensed danger. After listening for a few seconds, Raven dashed toward the door, with Jet right behind him. They worked together and pushed it open. When Raven and Jet stepped out, they saw Snow and Silver coming out from another door. Jet stood on Raven's head, Silver stood on Snow's head, and the four of them exchanged quick glances. Raven and Snow sniffed hard, trying to figure out a smell. Soon, as if competing, they suddenly bolted in the same direction—toward the door leading to the rooftop. At that moment, the rooftop door—which Caroline had locked when she left—was now wide open. In the apocalypse, Caroline always locked every door behind her, just in case. But the rooftop door was a regular door with a regular lock. The invisible intruder was good at locks—they opened the door fast. The little group immediately rushed to the rooftop. And there, a battle had already begun! Handsy and Medusa had been enjoying the midday sun. Suddenly, Medusa felt one of her branches being yanked hard! She tried to pull it back, but the branch was gone. Someone had chopped it off. Medusa freaked out and swung her other branches wildly, trying to hit the invisible intruder! Her branches were super tough, almost like metal. How could anyone break one so fast? Handsy noticed Medusa's anger and swung his big leaves too. But soon, one corner of Handsy's leaf was gone! The two trees spread out their branches, swinging around.But their attacks hit nothing, just air. "Moving trees, and they're somewhat intelligent. That's fun." A voice echoed across the empty rooftop, yet still, no one was visible. Raven and the others reached the rooftop. Raven and Snow sniffed hard, trying to find the intruder. Silver and Jet were already flying above, circling the rooftop. Jet yelled down, "What the heck are you? Show yourself and get ready to die!" Then Jet shot a fireball at an empty spot. "A talking bird? Even more fun," the man's voice said again. As soon as he spoke, Snow and Raven lunged at him.