Army of Two (EU)

There's not a great deal I can offer you in terms of how to get this achievement, it's all in the description, complete the third mission of the game on Contractor difficulty or higher, however you may find these videos of the third level handy, it'll help you get your bearings on any part you might be stuck on and give you an idea of what to expect!

*^{Credit to viconaz and LikeYOURMOM for the videos}