Reo was a Maker sent to hunt down Tain, a lost bioship of his species' creation.
Reo tracked Tain to Espero, a human colony, where he possessed the body of a small boy named Joshua to help him locate Tain. Reo later possessed Trix as Joshua's body had started to decay. Reo later found Tain and Reo moved his consciousness into Tain, where Reo was tricked by the Eighth Doctor and Fitz. Reo was erased from Tain's body while Tain escaped in the mind of a Mokey named Nessus. (PROSE: Halflife)