The Tharsis Refinery is where the Helghast refine all petrusite which can be used as fuel or arc technology, if it is weapon grade. Many experienced Helghast soldiers inhabit the place, as well as a large population of spiders and bugs.
The mission begins with Sev and Rico on a train that is heading for the Tharsis Refinery. After killing many Helghast on this train, they encounter the first and only non-hostile Helghast in Killzone 2. The only thing this miner says is "I-I'm not a soldier!" and also "I have to stop the train!". When the train stops, Rico and Sev split. It is unknown what route Rico takes. Sev travels through the refinery and has to fight the Arc Trooper, finding a VC5 Arc Gun on the corpse. After a while, Sev and Rico meet again in a control room, and get to the place where Colonel Mael Radec is holding the rest of Alpha Squad, Evelyn Batton, and a Scout Team CO. When Sev tells Rico to wait for his signal, Rico goes in anyways and kills most of the Helghast, Garza getting shot by a wounded Helghast. Radec escapes, and flies away with an airship just when Alpha Squad comes out of the refinery. Garza dies from his wounds here, and the mission ends.