From the Moebius Foundation base, Dark Prelate Zeratul discovered the location Amon was revived at was the Temple of Erris on the planet Atrias. Zeratul and Praetor Talis dispatched their forces to the planet, hoping to find how the protoss fit into the prophecy.
Zeratul and Talis secured a base planetside, and Highlord Ma'lash sealed the temple to finish his communing with Amon. Talis noted that due to the decay of the planet, vespene gas was leaking from fissures, and it would be difficult to find any natural geysers. Zeratul said they would have to harvest from these fissures when they erupted.
Zeratul also noted rock formations that covered natural vents of vespene gas. Should these be destroyed, Zeratul could mine the gas from orbit using the Void Seeker.
When enough forces were mustered, Zeratul and Talis broke through the Tal'darim defenses and destroyed the temple's door. This allowed Zeratul to slip into the temple while Talis stood guard outside to defend the inevitable Tal'darim counterattack.
The player spawns on the southeastern corner of the map, and they must fight their way to the Tal'darim main base. Even though it is impossible to harvest natural vespene, that does not mean that the player will be hurting for gas. Natural eruptions provide a substantial amount of gas, and destroying rock formations can provide a steady source of income.
Void rays will be essential on the harder difficulties, as creating a great number of them is the easiest way to content with the carriers and colossi that the enemy will deploy. When pushing out, attempt to expand to new mineral fields, especially if going for the mission achievements, as they will be useful in helping step up production.
Complete the "Ghosts in the Fog" mission in the Whispers of Oblivion Campaign
Acquire 3500 vespene gas from eruption sites during the "Ghosts in the Fog" mission
Destroy all enemy Nexuses during the "Ghosts in the Fog" mission in Normal difficulty