When you enter the Agroprom Research Institute area you'll notice a stalker ahead of you, calling you towards him. It turns out that Mole and his group are under attack by the military and he wants you to help them in the fight. Follow the stalker towards the first installation of buildings; once you get closer you'll be interrupted by a small in-game cutscene showing you the area ahead revealing a number of stalkers exchanging gunfire with soldiers.
On your way there may notice several artifacts in the surrounding area - you can pick them up now, if you wish to, or wait until you have defeated the first group military guys. You can also wait until you have completed the documents mission but I personally like to secure any artifacts as soon as possible.
As you close in on the first installation you'll get a transmission from Mole saying that they need help with defeating the military and you'll be given the mission Help the stalkers. Once you have defeated the first round of soldiers, you'll complete the mission and get a transmission from Mole saying that he's cornered in the yard (the central part of the installation). This translates into the mission Save Mole. You can take the time to loot all the bodies if you wish - as far as I know, the soldiers will not kill Mole so there's no need to hurry; also, once you have saved Mole more soldiers will arrive from the same direction you did - so if you don't want to have to deal with them, looting corpses now is probably a good idea. Most, if not all, of the soldiers are carrying Akm 74/2 rifles so if you are still using an Akm 74/2U now may be a good time to exchange that with it's bigger brother.
Once you have defeated the soldiers in the yard you can go talk to Mole; he'll thank you for your help, and then prompt you to follow him before the task force (more soldiers) arrive.
Mole will take you across the installation and out on the other side of the western wall. There he will stop by a hole in the ground and say that what you're looking for is around here. Talk to him to get some more, concrete information. Strelok and his group apparently had a stash and a base here but Mole doesn't know the exact location. I guess you'll need to head underground and try to find it for yourself. Once you have talked to Mole you will complete the Find information about Strelok and Save Mole missions, and be given a new one: Find Strelok's group's stash. When you're ready, head down the hole next to Mole.