You have to go to the shiny circle on the rooftop of one of the buildings.
Once you get there, you’ll watch a new cut-scene.
double-check that you’re disguised as a soldier or a scientist before you approach them.
It is very important, because according to received directives you’re able to’t get exposed.
Consuming one of soldiers will allow you to advance to the further part of this mission.
As for the infected, keep them on distance, because they can inflict damage only in melee fight.
Continue your walk in the company of other team members.
I suggest completing a new optional mission objective first.
You have to kill three infected with the grenade launcher.
Pass by brawler and run towards a larger group of mutants.
Shoot the grenade launcher before the infected scatter in the area.
Only after completing the bonus objective, start attacking brawler.
When you run out of ammo to the grenade launcher, look around for other such weapon.
Finally take care of standard infected.
Prepare for the fight with one hydra.
Watch out also for large objects thrown by hydra.
Keep fighting until hydra is dead.
After the battle begins, focus only on attacking brawlers appearing in the area.
Do not let mutants push you in a corner and perform many side jumps, thus avoiding damage.
After dealing with brawlers, eliminate standard infected.
You have to hurry up, because another hydra will soon appear behind your back.
In addition brawlers will join the fight.
Keep attacking the first hydra, but remember not to get close to it.
After eliminating first hydra, attack previously mentioned brawlers.
These monsters are not so tough, so you could use standard rocket launchers to kill them.
In the meantime watch out for pieces of concrete thrown by other hydra.
Finally take care of the second hydra.

You have to eliminate all mutants.
It will result in displaying a new cut-scene.
Notice, that one of the scientists is not dead.
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