Lu Chen was forced to join Bureau 749 and cut off the parasite with a scalpel. He gradually discovered that there are five levels of parasitism by alien beasts: parasitism, erosion, fusion, awakening, and arrival. Inside Lu Chen's chest was the only surviving "Experimental Subject Zero" - a "symbiotic" alien beast sealed by the human camp during the ancient war. While hiding himself, he investigated the truth about the ancient crack.
