 The Doctor and Peri arrive on Space Station D7 so the Doctor can receive medical help from scientist Dastari. Only to learn Dastari is in league with the Sontarans and he and his Androgum assistants, intelligent Chasini and the cannibalistic Shockeye have kidnapped The Doctor s second incarnation and conduct a genetic operation on The 2nd Doctor to discover the secrets of time travel and they find the Doctor s former companion Jamie McCrimmon left for dead on Space Station D7. Where the Doctor, Peri and Jamie traces Chasini, Dastari, Shockeye, The Sontarans and The 2nd Doctor to Seville on Earth, where Chasini plots to spread her malice through time and space.