In the world of Jack the Ripper and Sherlock Holmes, “Gaslight” London is a perfect place for mayhem amid cold comfort. When Aunt Alice, a wealthy opera singer, is murdered in the home she shares with her ward Paula (Ingrid Bergman), the girl is traumatized and sent away for a decade to the Continent. When she returns with a continental husband named Gregory (Charles Boyer), the happy couple sets up home in the same place where Aunt Alice was murdered. The post-traumatic stress rekindles in Paula who begins to think the house has creepy auras, including a strange darkening of the gaslights on occasion. She becomes forgetful, and dressed for a grand night at the opera, her husband informs her they went the previous night. Didn’t she remember? No, she doesn’t, and the smarmy maid (Angela Lansbury) doesn’t help much either. Fortunately, a neighborly detective (Joseph Cotton), smitten with Paula, does have an interest in cold-case, unsolved murders. Paula may be facing two options: her own murder or being committed to an insane asylum.