Quest giver: Ser Rickart
Survive the ambush
You have to survive the ambush set by five groups of assassins in different areas. You'll know if you've run into them since they'll talk to you and give you their names.
1. Past the bridge northwest of Gran Soren, leading to Deos HIlls
2. Outside the Ancient Quarry entrance
3. Mountain Cottage area
4. The stretch of road south of the mountain waycastle and abandoned storehouse
5. Outside Cassardis
You have to deal with the four groups first before getting an update telling you to go to Cassardis' gate where you'll have to fight and kill the leader of the assassins.