Stalker: Call of Pripyat → Quests → Latest Developments
Scientists ask you to find some documents located at the Jupiter plant. We go to the plant and find them. Seems like a simple task? Not at all. After you find the documents, you'll be attacked by a squad of mercenaries. The leader is armed (at least for me) with a G37 and wears an exoskeleton. After his death, you can take the PDA from his corpse and bring it to the scientists.
Interesting: mercenaries swear in the most natural way during combat. Not in a veiled way, as bandits sometimes do, but for real. Just listen.
Having received the documents and the PDA, they'll ask you to find them new security (if you come back in a couple of hours). The Dolgovtsy would be perfect for this; you just need to talk to their leader. The Svobodas could probably also be deployed to protect the scientists, but I'm not sure the scientists themselves would be thrilled with the Svobodas.
Source: gamer.ru
See also:
Pirate Invasion. Events in Terraria
Fallout Tactics: Mardin mission
Sulfur. Chemical Properties and Uses