Doctor who - the War Doctor 1 Only the Monstrous

1.2. The thousand worlds. With the high-ranking Time Lord Seratrix behind enemy lines, the War Doctor finds himself assigned to a rescue mission. But any room for manoeuvre is severely restricted by an area of space known as the Null Zone. Times have changed on Keska, and a countdown to destruction is beginning. But who are the Taalyens and what is their part in the great and terrifying Dalek plan?