After the death of Visari,Admiral Orlock,commander of the First Army,orders the Helghast to hunt down the ISA & have them either dead or alive.
6 months later after Rico's disappearance,The ISA hid in the jungle where Captain Narville sent Sev to restore the communication uplink,but it was intercepted by the Helghast. The ISA struggles against them,but half of them are killed and the other half,including Sev & Narville,are captured. Rico manage to save Sev along with Hooper & Jammer.
they attack the Helghan facilities in the area and learned that Narville will be executed by Jorhan Stahl,chairman of arms manufacturer Stahl Arms. The two disguise themselves to rescue Narville & the prisoners. They soon discover that Stahl has built his own armada armed with weapons powered by irradiated Petrusite,powerful enough to tear living organisms apart.
They quickly regroup with the ISA & fought against the Helghan Mech. After destroying it,The ISA went up to the spaceport. Aware of Orlock's plan to kill him after securing his weapons,Stahl kills him before launching an attack on the First Army,giving the ISA a desperately needed opening to steal several Helghast transports.
Stahl orders his flagship to warp to earth,but the ISA damage the warp coil,causing the ship to plummet towards the Helghan's surface. Sev fires the missle to destroy the vessel,killing Stahl. The resulting fallout destroys what remains of the Helghast. With the war over,The ISA returns to Vekta.