While Jack and Valerie are still unconscious, Kriegel abducts them.

Jack wakes up to find himself in a helicopter with Kriegel and Valerie. Jack is thrown off the helicopter by an elite guard and Kriegel sarcastically says, "Survival of the fittest, good luck with that!" On the ground, Jack finds a tossed rifle with only 10 rounds of ammunition. He needs to rescue Valerie a third time, and his needs to cross the security perimeter like Trigens did. Upon reaching a mercenary weapons depot, Jack finds his arm turning green, and Doyle states that the antidote should be able to deal with it, but the explosion may have filled the air with mutagenic substances that the serum developed by Dr. Kriegel should have a way to deal with. Jack decides to go straight to Kriegel for treatment.

Since the mercenaries are fighting Trigen, Jack has little trouble climbing up the slope of the volcano to the headquarters
Kriegel has apparently discovered a method used to stop the eruption and use the flow of lava to generate electricity. Jack asks Kriegel, who has mutated after being injured, for an antidote. Kriegel states that there is no time to prepare the serum and that Jack will be a specimen in an hour, not to mention Valerie. Then Doyle appears nearby implying that there is still a remaining serum. Deciding that he will not leave the island until Doyle has found the antidote, Jack takes a weakened Valerie to the docks, and then, he returns to the factory.

At the crater, Kriegel's lava utilization system is damaged and an eruption is imminent
Jack escaped before the volcano erupted, using blast doors to protect himself from harm. He and Valerie use a sailboat to leave the isolated island, and the eruption destroys what is left of Kriegel's laboratory. Jack treats Valerie with the antidote he has found. In the ending animation, Valerie looks at a thick folder of documents and two discs tied together labeled "Project Crysis" (or "Project Mutant" on the French version of the game).

In the Xbox version of "Crysis: Instinct", the main character Jack has the ability to bestialize.
In Crysis 2, the villain "Jackal", an arms dealer that the protagonist is hunting, is the same as Jack