He was injured on Simia KK98 and encountered an incarnation of the Doctor. Following this, he was taken by the enemy, who, using Celestis technology, changed him from a liquid-based lifeform (as a Gabrielidean) to a Shift. He attended the auction for the Relic on Earth with the aim of making sure none of those invited obtained it.
The Doctor was able to trap the Shift in his mind and trick the Celestis into marking it as their agent when they attempted to mark him. As a result, not only did the Doctor obtain the Relic by tricking the other attendees into thinking that the Relic was now a temporal paradox (as the Celestis had marked him now, rather than immediately before his death), but the Shift was driven mad as it was torn between its new status as an agent of the Celestis and its original role as an agent of the enemy. (PROSE: Alien Bodies)
Because of this madness, the Shift was put in a zoo of ideas on Mictlan. It escaped the zoo by making one of the Celestis' servants think about it and pass it on to others as an idea, but it only escaped Mictlan by boarding one of the Great House's timeships while the realm was being attacked by the Memeovore. Together, the Mictlan refugees and the fugitive timeships found a safe refuge, either in the very early universe or another universe entirely. (PROSE: The Book of the War)