Greg was one of several Cardiff residents who became influenced by an alien computer. While under its control, he would share personal information with complete strangers. When Torchwood Three attempted to analyse the source of the strange behaviour, the computer interpreted this action as an attack, and sent its heralds to locate and kill its enemies. When John Davies was killed pursuing Jack Harkness, Owen Harper, Gwen Cooper and Tony Pratt, Greg summoned Tommy Kincannon, Vic Royce and Linda Sosa for assistance. He pursued Gwen and Tony to a school, where they knocked him unconscious and handcuffed him to a radiator. Greg's mind was freed when Torchwood shut down the computer influencing him. (AUDIO: Everyone Says Hello)