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Great One is a StarCraft II short story written by Alex Irvine, designed to tie-in with Heart of the Swarm. It focuses on the ultralisk. The story was later collected in StarCraft II: War Stories, and relates to the narrative of Project Blackstone.
Marine platoon Torch Seven drops onto the faraway planet Vygoire to find out what happened to a science outpost there. The planet is supposed to be zerg-free, and it is...mostly. But as it turns out, Torch Seven has enemies other than zerg.
Doakes and his squad, Torch Seven, landed on the planet Vygoire in order to investigate a research base that had failed to report in for nearly six months. They found the base, but it had been destroyed and in a state of disuse, and completely abandoned. The squad found research into a psychoactive spore and strange graffiti on the walls, all of the same symbol. Later in the sweep, he found the remains of four humans.
They moved into the jungle to see if the research team moved in there, and found the remains of the battle against the zerg that occurred two years earlier. Torch Seven used their HPIGNUs to scan the planet's atmosphere, and found it safe. They contacted the Scion, which had to quickly leave orbit for emergency escort duty. The squad continued their hunt for the science team, and found more of the symbols they had found in the lab carved into trees, followed by human remains. Later, they came across huge, quadruped tracks.
Suddenly, one of the squad began to panic, shout random coordinates, and scream about a Great One. Suddenly, an ultralisk came out from the brush, killing Singh and Morrison. Torch Seven shot what it could into the zerg beast, but to no avail. The squad suffered thirty percent casualties before Doakes ordered a full retreat. They backed into a ravine the ultralisk could not get through, and it retreated as impaler rounds began to get through its carapace. He reorganized his squad, who were unnaturally panicking. As Doakes was telling this story, he began to rant and rave about the rage he felt, which caused Langridge to give him another sedative.
They contacted the Scion, which was on its way, but would refuse to send dropships until the ultralisk was taken out. Torch Seven was then ambushed by spears, which did nothing to their armor. The source of the spears was the scientists, who were ranting and screaming about the Great One. They pulled one aside, who said he had to get to Doctor Gerhardt van Rijn for the ceremony of the Great One. Doakes demanded he be taken to see the doctor. Just then a woman, who was Vera Langridge, stood up and told Doakes about their situation. She said the research team were studying the spores on this area, but they had started going insane because of them, but that she was immune. However, she said that Doakes and his squad were all infected.
They approached the village, where van Rijn told them they needed to leave the planet, and the Great One was coming for them. Doakes then figured out that the Great One was the ultralisk they encountered earlier, infected by the spores. It burst out of the brush, and the infected cultists ran toward it, the creature devouring them en masse. Torch Seven escaped, and ran toward the abandoned lab.
Doakes began raving again, and the scientists debated over giving him another shot. Vera Langridge then revealed that the spores meant he could commune with other infected, and by extension potentially the zerg swarm.
They moved to the lab, but were confronted by Van Rijn and a group of his cultists. He stated they had a ritual tonight, when the two moons of the planet intersected. Langridge revealed the spores triggered parts of the brain that predispose humans to ritual worship. Doakes told his squad the only way they'd get off the world is if they killed the ultralisk.
The squad put together a bomb from vespene gas stored in the base, putting it under one of the rockfaces. They hoped to crush the ultralisk under a mass of rocks. The cultists attempted to stop them through human chains and laying down near the bomb sites, but they were tossed aside with relative ease. Doakes then went down to the ritual, and heard the ultralisk coming. He lured it to the vespene bomb, and set off the charges, collapsing the ravine. Jouvert went to check if the explosions had killed it, then was chopped in pieces as the ultralisk arose from the rubble.
The squad opened fire on it, with the cultists rushing up to be killed by their Great One. Doakes was contacted by a dropship, who told him they were en route but wouldn't land until the ultralisk was gone. The ultralisk knocked Doakes over, then ran toward him, but Doakes managed to pierce its armor with a lucky shot, and wounded it. Van Rijn ran up to it, but was sliced into pieces. The remainder of the squad kept opening fire on it, in spite of the cultists rushing to it. Doakes then stated that he could feel the ultralisk and its thoughts, before rambling again about how Langridge was infected too.
Langridge then talked to one of the commanders on the Scion, who said they were nuking the planet from orbit and Doakes would be the only sample they had. She said she had orders, but was not at liberty to say who those orders were from. The commander protested, but Vera insisted that she was doing as she was told, and that Vygoire was no longer a problem.