Birthright
Nigel Robinson
 After the TARDIS malfunctions and then explodes, the Doctor's companions find themselves in two different time zones. Bernice is stranded in the East End of London of 1909, where a series of grisly murders is occurring blamed on Spring Heeled Jack, while Ace is trapped on the planet Ant'ykhon fighting alongside guerrilla fighters against alien oppressors. Ace discovers that Ant'ykhon is actually the planet Earth, 22,000 years in the future and devastated by rising temperatures. The Charrl, an insect-like race, now inhabit Earth. They have been using an unstable trans-dimensional link called the "Great Divide" to travel to Earth's past in order to escape from the dying planet. Once there they implant humans with their eggs, but inadvertently kill them, causing the murders blamed on Spring-Heeled Jack. Since the Great Divide is unstable, any Charrl that travels to the past eventually crumbles into dust. Back in 1909, Benny is scratched by one of the time-travelling Charrls and is implanted with an egg. This has the effect of placing her under the control of the Charrl, causing her to replace the missing Time Vector Generator in the TARDIS and reunite it with its other half in the future. This also stabilizes the Great Divide and allows Jared Khan, a Charrel agent, to attempt to use the Great Divide to give him immortality. The TARDIS time rams its other half and sends it and Khan back to Siberia 1908, where it explodes, causing the Tunguska event. In the far future, Ace and Benny are aided by Muldwych, a mysterious hermit and former ally of the Charrl. He uses the TARDIS to entrap the Charrl inside one its interior dimensions, then sweeps the Great Divide over London, clearing it of Charrl and their eggs (and curing Benny). But when he tries to use the TARDIS to escape from his exile on Earth, the TARDIS expels him from the ship and returns him to Ant'ykhon. The Doctor emerges from the interior of the TARDIS, claiming to have been asleep in his room the entire time (but see Iceberg for details).