Infection

Infection is the third mission in the game. It takes place in the Vietnamese countryside on Day 1 at 1200 hours.

Walkthrough
The mission begins with Nate having another vision of his brother, this time running through a series of underground tunnels. Nate regains consciousness underground in the same set of tunnels. He begins his search for Cal, coming across the bodies of several mutilated G.Is and Sgt. Franco, who has had his legs torn off by whatever dragged him out of the church and is now bleeding to death. A little while later, Nate comes across two live Americans. The first is seen running through a passageway holding a flare. He yells at Nate to get away from him, before running off and falling into a punji stick trap.

The second man is encountered running away from an underground lake. He calls that something is "in the water," but the protagonist will find nothing other than a dead G.I and continue on unharmed.

Nate finally makes his way out of the tunnels, leaving behind a third G.I who tells Nate not to touch him and is cowering in a corner. The protagonist walks a short distance through the jungle, before being surprised by three U.S soldiers demanding his name and number. Nate, recovering from the shock of everything he had seen underground, tells them his name and then joins them in holding off an attack by NVA troops. After several minutes, another soldier will order Nate to follow him, and the pair will make their way through a network of trenches in the midst of a full scale NVA offensive. During this retreat, Nate will have the option of saving his guide's life when an artillery shell flies towards them. He can either push the man to the ground to avoid the explosion, or leave him where he is and watch as the man is blown apart. Regardless of the player's choice, Nate will continue on towards an aid station, suddenly being knocked out by another artillery explosion.

When he awakes, Nate finds himself staring up at a young woman named Serena. She will talk to him flirtingly for a few moments, before being interrupted by her 'agent' Rupert Zideck. Zideck attempts to distract her from Nate by reminding her that she shouldn't be taking part in the combat and that "this isn't a game." Serena seems to be unconcerned with what her manager thinks, and the two are in the midst of an argument when they are interrupted by an American soldier, who warns them that the NVA is about to make another attack. Nate, Serena and the G.I will hold off the enemy onslaught while Zideck cowers in the background. After a while, they will be forced to retreat as the hopsital is shelled by rocket barrages. As Nate follows his squad mates through more trenches, he is stopped by an American officer, who orders him to provide covering fire while he and another soldier transport a captured Vietnamese officer to a waiting helicopter. Nate uses a Heavy Machine Gun to hold off NVA attacks, and after completing his assignment returns to making his way out of the trenches.

Rounding a corner, the protagonist is suddenly surprised by the American officer, who is frantically running away and shouting that the enemy prisoner has gotten loose and turned 'rabid.' Seconds later, the crazed NVA officer jumps down into the trench and hurls himself at Nate. The player must fend off his attacks before managing to push the attacker off and impale him on a wooden stake.

Fighting through more NVA soldiers, who have now succeeded in overruning the trenches, Nate enters another series of tunnels, encountering several Infected and more enemy troops inside. Finally reaching the exit, Nate witnesses Serena being torn apart by zombies while other soldiers attempt to save her. Nate and a small squad fight their way along a river bank, where the protagonist is told that there is a boat waiting to take him to a safehouse. Nate boards the transport, and the boat speeds away from the shore while more infected continue to fight the G.Is left behind.