They can also collect Protoss relics and Zerg genetic samples for their scientists to research, unlock more unique benefits for certain units. Using credits earned from doing missions, the player can buy upgrades for their units and hire mercenaries to supplement their standard forces.
Gameplay in this game features the Hyperion as the mission hub for Raynor and his men. The dark templar gasps out a warning of something dire he has learned, and gives Raynor a crystal containing the memories of what he has seen in the past four years - the universe is in peril, Kerrigan is the key to saving it, and soon Raynor will hold her life in his hands. In-between retrieving alien artifacts, helping out people fleeing the Zerg, and trying to find a way to get an edge on Arcturus Mengsk, Raynor is contacted by his old friend Zeratul. As Raynor's right-hand man Matt Horner lays out, the situation isn't good - the Zerg are invading Terran space, breaking their four years of peace, and the Dominion is pulling back its troops to protect the core worlds.
