As per the morally ambiguous research carried out at PAX, Gruu often portrayed himself as one possessing intellectual dispassion. However, with the delivery of a sample of creep for viral experimentation, cracks in his facade started to appear. Regardless, he was ordered to administer the virus and thus retired to his quarters, his memory taking him back to the death of the researcher Nubas, who had injected himself with genetic accelerant, only to perish due to missing a helix strand. Gruu could not help but ponder the morality of committing genocide against another species, whether the researchers at PAX were, like Nubas, accidents waiting to happen.
However, an accident did still occur, specifically the creep sample "erupting" when zealot guards Golarath and Ruom went to extract a tissue sample. As it grew, Golarath began disfiguring himself, eventually falling to his own psi-blades, while Ruom fell into catatonia, his mind unreadable. He was taken to an isolation unit, while Gruu, like the rest of the scientists, felt their link to the Khala become "foggy," their memories of Nubas blurred, some believing he'd experimented on himself, others that they had carried out forced experimentation. Gruu was of the latter, though still knew that it was a "rogue memory."
Seeking to clear his mind, Gruu sought solace in the installation's vivarium, finding himself joined by fellow scientist Wa'Rak. His co-Furinax claimed that Nubas' presence had returned to PAX, that they had to "prepare." Although Gruu initially dismissed Wa'Rak's outburst as a symptom of the psychological shroud that ailed the facility, he began to wonder if Nubas' experiments had perhaps elevated him to a state beyond death. However, before he could ponder further, a disturbance shook the facility, said disturbance destroying the stargate that connected it with the rest of protoss civilization. Akam suspected sabotage and noticing that Wa'Rak was missing, the group went to investigate, only to find that he'd committed suicide in a manner similar to Golarath. It was at this point that Ruom was revealed as the culprit, having become infested. Akam and the scientists Forthum and Jhas were killed almost instantly and Harrum wounded. However, via telekinesis, Gruu managed to activate the teleportation mechanism of Ruom's power suit, buying some time.
However, the time quickly ran out, Harrum falling to Ruom and horrific visions clouding Gruu's mind, courtesy of the mutated, rapidly growing creep. As a last ditch effort, Gruu shattered the cooling crystals with a laser scalpel, freezing PAX and everything in it, including himself.