- No Stone Unturned (25 GS): Investigate a sinister conspiracy.
- Under Pressure (50 GS): Uncover an ancient secret.
- Conspiracy Theorist (25 GS): Use clues to pinpoint the exact location of an objective.
- Family Matters (25 GS): Rescue a civilian from Reaper forces
No difficulty-specific achievement. It kind of seems like they're all unmissable story milestones.