Save Theresa from the Cumans.
To unlock this achievement you must save Theresa from the three Cumans attacking her during the main quest ‘Run!’. You will find Theresa to the right of the road as you escape Skalitz. You can either whistle near to the Cumans to distract them, or attack them directly.
Note: It will be difficult to kill the Cumans at such a low level, so it is a good idea to run away once you have their attention.