The Terra Conspiracy
It all began when your contact sent you to a lab to bust up a raid by the Devouring Earth. After routing the creatures, you spoke with Dr. Steven Sheridan, who determined that the creatures had used the lab to manufacture drugs that hamper the body's ability to fight off infections.
Seeking more information, you went to a front company owned by Fauna First, the eco-terrorist group aiding the Devouring Earth. There you discovered that the creatures had turned on the activists and kidnapped one of their members, Tanya Tyler. Your first attempt to rescue Tanya yielded only a map,scrawled on a love letter written to the young woman from the Devouring Earth's leader, Hamidon.
Tanya's map led you to her new location, and you learned her story: Tanya knew Hamidon before he was the master of the Devouring Earth. She told you that the creatures were probably created by a sentient bacteria Hamidon developed, a bacteria he called the 'Will of the Earth.'
While your contact took Tanya to a safehouse, you went out to stop another Devouring Earth raid. You defeated the monsters, but not before they made off with several cases of fertility drugs. Your contact proposed a theory: the drug thefts, Tanya's kidnapping, Hamidon's strange attraction to her: all pointed to one conclusion. Hamidon intended to change Tanya into a Devouring Earth matriarch, a creature capable of breeding more Devouring Earth creatures.
While you were at the lab, Hamidon's monsters recaptured Tanya. You rescued her again, but not before the Devouring Earth infected her. You took her to a lab for treatment, but she transformed into a Devouring Earth monster and escaped, leaving you no choice but to track her down and defeat her.