At some point before the Peloponnesian War, Pleistos came to work for Chrysis, and via her the Cult of Kosmos. He agreed to watch the Sanctuary of Asklepios for Chrysis, and especially the priests, who had all been forbidden to talk to the 'Eagle Bearer', the Spartan misthios Kassandra.
Behind the scenes
Depending on the dialogue choices made in Written in Stone, Pleistos will either have Timoxenos killed, leaving his body at the meeting site for the Eagle Bearer to find before confronting them. Otherwise, Pleistos will confront them both, and Timoxenos will spend the rest of the game under some olive trees nearby.