Go to the house and open the door. Brenda will have Katjaa at gunpoint at the bottom of the stairs. Move forwards until Brenda tells you to stop. Then talk to her and she will move slowly backwards up the stairs. When she stops moving, start moving forwards again. Keep repeating this until she is attacked and you and Katjaa run outside.
You will then end up in a fight with Andy.
*** Spoiler - click to reveal ***As you start to walk away at the end, he will tell you to finish it. Either kill him or walk away. Which ever way you decide, you will get your achievement.