Alright guys, as this is a story mission, you cannot miss it so a guide isn't all that necessary, nevertheless I will give one, just click the spoiler button to see it:
*** Spoiler - click to reveal ***After completing the level 5 mission False Oracle, your next story mission will be to talk to your ally Hepzefa about leaving Siwa. Once you talk to him the achievement will pop.
Let's keep cheevin' together!