I'll Never Forget You (1951)

An American physicist, Peter Standish, lives in London in an inherited flat on Berkeley Square, unchanged from its 18th century appearance. He's researched his ancestors and the flat, and he believes somehow he will travel through time, if only briefly, to 1784. A lightning strike transports him, and he finds things disturbingly different than he expected: disease and social conditions appall him, and, in this Age of Reason, his speech, manners, and knowledge frighten rather than interest all except one young woman, Helen, the sister of the woman he's to marry. He sets up a laboratory in the hopes of hastening progress, and he tells her his secret. Does love or Bedlam await?