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This achievement is missable and is earned for successfully completing all of the objectives in Mission 16, Stopping Marchenko, and Mission 17, Protecting the Future, in a single playthrough.

After the long cutscene with Miller at the end of Mission 15, you will be tasked with either stopping Marchenko (Mission 16) or saving the delegates (Mission 17). For this achievement, it doesn't matter which you choose first, just know that you have to move quickly! Assuming you decide to take on Marchenko first, keep in mind he will activate the bombs after ten minutes have expired, so move quickly to his position.

Once he has been defeated, you can move onto rescuing the delegates for Mission 17. Again, there is another ten minute timer here. You must have defeated Marchenko and reached the delegates in under ten minutes or else they will be poisoned. So long as you complete this final mission under the time constraint, you will unlock the achievement during the final cutscene for having accomplished both feats successfully.