Death stalks the fogbound streets of Victorian London: young women are going missing, horribly mutilated bodies are found floating in the Thames and criminal gangs terrorize the innocent. At the heart of this tangled web sits the mysterious Li H'sen Chang, sorcerer and hypnotist, and his grotesque sidekick Mister Sin. The Doctor dons deerstalker hat and cape to seek out the sinister force lurking in the shadows of the metropolis, for the Talons of Weng-Chiang are reaching out to shred the human race.

In the far future, freedom fighter Roj Blake, framed by the all-powerful but corrupt Galactic Federation, escapes his captors from his sentence to a harsh penal colony and, helped by a handful of fellow convicts and armed with a superbly-equipped alien spaceship, sets about restoring freedom to the galaxy.