This daily mission is given by the Junior and regular Agency Handler from the office in Rome Blue as well as the office in Athen. It requires you to travel to ICC and enter Serenity Island and speak with the Rookie Exterminator to get things started.
This is a timed mission, you have 15 minutes from when talk to the Rookie Exterminator to complete your mission.
To get to Serenity Island, go to ICC and look for this entrance:
Entrance to Serenity Island.
From where you zone in, run down the hill. You should see the Exterminator on the edge of the city area.
Talk to the exterminator to start your mission.
Rounding up the Rollerats.
Basically, you now need to grab agro from the rats and herd them to the special structure located near the exterminator. You need to get 100 rats to this structure.
If during the mission you are curious how many roller rats you've killed you can ask the Rookie Exterminator. The Rookie Exterminator will inform you that you have completed your mission by shouting the following when you have pulled 100 or more roller rats to the extermination system:
Rookie Exterminator shouts: ...and that one was 100! You are done! Get over here and talk to me so we can get out of here!
Rookie Exterminator shouts: You are finished...get over here!
Telling the exterminator that you killed 100 rats will update your mission and let you report to the agency receptionist to claim your reward. You can get out of the zone by heading back up the hill to a paved area where the ship is. There should be a blue portal on the ground which you can stand on to be teleported back to ICC.