You star off on a plane,being shipped to Somahara island for tempoary Vacation,however,before arriving,the plane get's shot down (AT low-altitude,thankfully) and the team awake to find thereselves in a small beach,before noticing a man sitting on a bench,whimpering,they approach him,and,as expected,he is infected,luckily the survivors kill him before he alerts a horde.
The first real mission kicks off after that,the survivors are forced to locate safety (Survivor bases) nearby,on there way they have two choices,go through the town or walk through to cliff-forest near the town,either way,a tutorial plays out demonstrating new things:Such as enivormental traps,and their use/danger,as well as the new infected and the ability to sneak past common infected.ALternatively,the tutorial can be skipped.
Outside of the survivor base,the team faces their first horde,using tier 1 weapons to defend theirselves against the horde and the new infected,they get to enter the small survivor base.
As the story goes on,the team uncover the reason behind the infection,whos making new infected,and CEDA's involvement.Subtle clues lead the survivors to Military Base Alpha Congo,where they fight the first Boss Infected,The Cerberus,a fearsome three headed dog infected that has grown to the size of a tank.
After the encounter with the Cerberus.The Team start encountering Advanced Infected,these are stronger,faster and nastier than Common Infected,and are only attrracted to Stun Grenades.These prove a challenge for the survivors,especially as they discover the infected can be controlled by Leader Infected,who can use firearms,throw explosives,and command other infected.The team hunts down and kills all of the important leader infected,causing a Civil War Between the Common Infected and Advanced Infected,and the squad choose how to and when to tip the balance of the war.
They attempt to engage it,but are almost killed untill a Kraxon alarm sends HADES away.They are however,confronted by new Alpha Special Infected,which are some of the original infected,and are controlling numerous infected,the squad can kill various alpha special infected to tip the balance,which ultimately affects the ending.
After killing the desires Alpha Infected,a new boss infected appears,The Juggernaut,The Squad are forced to collapse buildings on it to weaken its armor,before letting frank punch it,after defeating the juggernaut,it melts into a normal infected and drops a Disc.
The Squad take this to Jacob,in Survivor Base Alpha,who analyses it,revealing Doctor Comaher is responsible,the squad track him down to a base under SomaHara Volcano,but he escapes and lets HADES engage the survivors.They have a very tough fight,ultimately culimating in frank revealing his infection status and almost killing himself to kill HADES,which he does,by snapping it into and then throwing it into an acid pit.
The squad,after fighting HADES,follow Comaher to the top of the volcano,he almost transforms,but his shot rapidly by the survivors.
The game ends in two ways.If the survivors let the Advanced Infected win the Civil war,SomaHara island is nuked.If the Player lets the Common Infected win,the island is just cleansed of the infected,and the island returns to its former state.
If you finish the Game on Freakin' Insane,WolfSquad's new lives are revealed:Frank became a Coach for the worlds leading Olympic team and in free time became a boxer,Daniel remained as a Military Sniper and became a leader of SomaHara military,Linda opened a Gun-Shop and James got his arm ripped off and now lives a crappy life.You also get a small,moving view of all the Locale's you visited,ending with a shot of HADES corpse,which begins moving,before the game cuts to black,a grumbling is heard along with voices,and then the game ends.
And SixDog?He ascended to become the personal Guardian of Five Dog,which is seen in the next game,TES11TY.
Also,if you look closely during the scene where Nitpicker looks up at the sky and you watch it form his view point,the faces of the Developers can be scene in the clouds,looking down on Nitpicker in a Triumphant way,rather pointless,but quite entertaining.