This is a Side Quest in Hades (Act IV). Epigenes, a guard found on the stairs in the Epirus - Refugee Camp, next to the spot you teleported to from Medea's Grove, tells you that the City of Paseron has been sacked by non-human beings. Now he is looking for help to fight back and rescue any surviving humans.
After receiving the quest from Epigenes, simply follow the road to the northwest to get to Paseron. You will bump into another guard, Theogenes, at the city gate (yellow cross in the image).
Talk to him and he will ask you to rescue the refugees. There are several small groups of them in the area northwest of the city gate. Just follow the quest markers on the minimap to find them. Keres surround the refugees. Kill the 5 groups of Keres which are marked as quest monsters (sparkling white circle around their feet, purple monster name. Green dots mark their locations in the pic) to set the refugees free.
Once you have freed all of the refugees, talk to Theogenes to receive your reward.