You are out looking for supplies with Kenny in town. He goes up a ladder which breaks and you have to find another way up. Use the winch on the jeep and attach it to the trailer. A woman then comes out of a building screaming.
You must decide whether to kill her and out her out of her misery, or leave her to draw walkers to her, buying you more time to loot the drug store. Which ever way you choose, you get the achievement.