Alpha Protocol

This achievement is called Friends Before Strangers and is awarded towards the end of the Rome mission sequence. Although it is a story achievement, it is missable. Spoilers ahead:

The last mission you're assigned in Rome is to investigate a museum where Marburg has planted a bomb. You'll be forced to choose whether to save the civilians and go after the bomb or to rescue Madison who has been captured by Marburg's men. You make your selection by going to either the East or West Wing after helping the security guards.

Go left into the West Wing to save Madison. After progressing a little further, an elevator will open and she will emerge, held at gun point by Marburg's goons. Successfully kill the goons before they can kill Madison (the pistol's chain shot works well here) and the achievement will unlock whilst a cutscene of her release is played.

During the last Rome mission, towards the end you will reach some stairs in the middle of a room with a fork in the hallway, two paths clearly labeled West Wing on the left, East Wing on the right.

*Make a save file right at the fork (thankfully checkpoint is right there) and go to the West Wing, continue to play out the level and it will unlock. Reload the checkpoint and follow the East wing for the other achievement,


SPOILER-
be weary of your choice depending on how your playing out the story, Madison will die by taking the East Wing. Reload with save point listed above baised on your playthrough type. (Thanks Omegalite for typo)