Here is the full list of all 48 Heathen - there are The sons of the law achievements.
Discover this place
Kill sick porters
Find this item
Kill weird rats
Complete the tutorial
Kill soldiers of the Faction 12
Kill heavy guards of the faction 12
Kill KERAS
Kill sergeants of the Faction 12
Kill aquatic creatures
Kill lunatic rats
Kill shamans
Kill screamers
Kill crippleds
Kill armed guards upgraded
kill stinkys
Kill spearmans
Kill diggers
Explode smart moving mines
Destroy S.M.M Machines
Kill flamers
Kill porters
Kill the heavy porter
Kill voices of the bats
Kill Facelesses sentinels
Kill facelesses guards
Successfully learn stealth