Set in the year 2005. John Raimi is a civilian scientist and a member of a counter-terrorism team sent to investigate the Volks Corporation. After meeting up with his best friend Bryson, Raimi and the team of marines take over the science facility and are forced to battle their way out. On the way out, a monster takes the head off of one of Raimi's squad members, and the monster is unlike any living thing ever seen before. At the end, one of the agents seemingly becomes possessed and kills the marine team with the exception of Raimi (he just gets badly wounded and later finds Bryson is still alive). He is captured and his spirit is torn from his body by one of the secret experiments. Soon after, Volks, the leader, puts Raimi into a machine to brainwash him (a fact that returns later). However, a young girl no older than 7 or 8 years of age, blows the machine's power to save Raimi, who he gets help from repeatedly. He now must wander the Volks Corp. while trying to get his body back. Raimi can take over other humans, animals, and even machinery to achieve his goal. He has to battle an unknown environment, dangerous hostiles, and save his best friend from the same experiment he was exposed to.
The walkthrough is laid out by linear objectives and then stages so you will know how far you need to get before you're allowed to fail.