In Victorian London, someone is killing prostitutes, someone the police have dubbed ""Jack the Ripper."" On the face of it, John C.V. York (Cary Elwes) is a likely suspect. A once-respected doctor who sunk to absinthe and laudanum addiction after his misdiagnosis killed the young daughter of a Duke. He retains a connection to polite society thanks to the devotion of Lady Ellen Chamberlain (Clare Sims), who loves him and hopes to marry him. But, he is also a habitue of the seedy district where the killings have taken place and has the medical knowledge to make the precise, surgical cuts that are the Ripper's modus operandi. But, this Jack is not the killer. Instead, he is a witness to the strange alien force that inhabits the prostitute's bodies, leaving them drooling a strange green bile, and then kills them when it jumps to another host. After seeing the alien force kill one woman, he does battle with a prostitute named Lizzie Stride, whose body has been taken