Cooke was part of a crew going to the forbidden planet of Orriv. He was worried about tracking down The Network because Frye didn't have a full plan, and that she wasn't going to give them his share of the money. He was possessed by the Network and killed. The Network used his mind to try and offset the voices in his head. The Tenth Doctor got the Network to let him go. (AUDIO: Echoes of Extinction)