The Bodysnatchers

It is London, 1894. Amid the fog, cold and degradation a gruesome business is being conducted: bodysnatchers are at work — bodies of men, women and children are being stolen from their graves for the sinister purpose of a mysterious gentleman.
When the Doctor and Sam arrive, they are witness to a horrifying scene in the evil-smelling fog: something rises up from the filthy waters of the Thames and devours a man — a man terrified for his life and on the run from the devil himself...
Teaming with an old friend, pathologist Professor George Litefoot, the Doctor is determined to get to the bottom of the mystery. Together with Sam, they discover there is a far graver threat facing London than just earthly grave robbers. Deadly alien beings the Doctor has encountered before are at work, and they bring a whole new twist to the word 'bodysnatchers'...
Featuring the Zygons, who battled the Fourth Doctor on TV in Terror of the Zygons