Closing in on the goal of time travel, the Androgum and Sontarans get set to double-cross each other. With Peri and Jamie alternately in danger of winding up on the bill of fare, the decision is made to genetically transform Doctor No. 2 into an insatiably carnivorous Androgum, which causes Doctor No. 6 to develop a sudden taste for house cats as he races to not let this change become permanent.