Gaslight (1944), an American film noir, directed by George Cukor and starring Charles Boyer and Ingrid Bergman, is based on a 1938 play by Patrick Hamilton and a remake of a 1940 British film of the same name and follows the story of a young woman whose husband slowly manipulates her into believing that she is descending into insanity. Significantly, the film opens with the image of a London lamplighter igniting a gas streetlight in the foggy Thornton Square, while another person reads a headline, Thornton Square Murder. The gothic, psychological thriller with the compelling storyline and the carefully created tense atmosphere throughout the film, added with the frequent dimming and flickering of the gaslights in the room of the leading lady, won the heart of the commoners and the critics alike, making the film was a huge box office success.

The story of Gaslight is about Paula Alquist, orphaned at birth, living with her aunt, the famous opera singer Alice Alquist in a Victorian mansion at 9 Thornton Square, who had to leave the place in black mourning clothes and taken by horse-drawn carriage from the house and was sent to Italy to live with her aunt's best friend Maestro Mario Guardi, a teacher of singing, after Alice Alquist was murdered during a burglary.

Ten years later, following a brief two-week whirlwind courtship, she marries the pianist Gregory Anton, who was once an accompanist of Alice Alquist and unknown to Paula her murderer.

After spending an Italian honeymoon at the Hotel Del Lago, while discussing about their plan of living, Gregory insisted that he had always wanted to settle down in London and Paula suggested to live in the townhouse, her ancestral childhood home at 9 Thornton Square that she inherited from her murdered aunt, although she did not visit the place in a decade.

After shifting into the three-story, claustrophobic mansion on Thornton Square in London, Paula began going through her aunt’s dark bedroom on the second floor with the furnishings draped in dusty sheets, representing the painful memories of the past.

In the room she found a single glove, telling Gregory that her aunt gave the other glove to a great admirer long ago. However, she became momentarily upset as she remembered how she found her aunt's murdered-strangled body in front of the fireplace under her regal portrait. As she grappled with the memory of her aunt's murder, Gregory suggests storing Alice's furnishings in the attic, which eventually becomes the room full of mystery, like so many Gothic tales. Nevertheless, when Paula found a letter addressed to her aunt from a man named Sergis Bauer, Gregory instantly snatched the letter from her hands, reacted violently, but apologized later for his rude behaviour. He also hired a young maid, Nancy, with specific instructions to never bother her highly strung mistress about anything.

However, Paula becomes tormented by several strange events, such as the footsteps and noises from the supposedly empty attic when Gregory is not home and the mysterious dimming of the gaslights in her room, apparently suggesting that gas is being used elsewhere in the household, although the old housekeeper denies lighting any new lamps during the night and Gregory rejects all as her imagination. In addition, Gregory flirts with Nancy, whose disdain for his wife also worsens Paula's tormented nerves. Soon, Paula almost reached at the breaking point by her husband’s continuous allegation about her forgetfulness.

During their visit to The Tower of London, when she was unable to find an heirloom broach, gifted by Gregory, it was ultimately found in her handbag. Gregory also insisted and tried to convince her that she is responsible for a missing painting, hiding it unknowingly and she is too unwell to be in public.

Eventually, one day, when despite his best efforts, Gregory failed to prevent Paula from attending a party hosted by her old family friend, he accompanied his wife, but accused her in the gathering of stealing his watch, searched her handbag and found it there. This was too much for Paula, who could not take it anymore and became hysterical in front of the guests. After taking Paula home, Gregory angrily claimed that her mother died in an asylum and that the letter from Sergis Bauer that she supposedly discovered, never existed. This time, doubting her own sanity and scared about her fate, Paula broke down in apprehension.

In the meantime, one day, Inspector Brian Cameron of Scotland Yard noticed Paula at her front door and was struck by her uncanny resemblance to her famous aunt, whom he admired since he was twelve. He was also informed by Miss Thwaites, a gossipy elderly lady of the vicinity, about something mysterious and odd details of the couple, living in the Alquist home. Sympathetic to the anxious attitude of the young woman, added to the information gathered about them from the lady, led the detective strongly feel that something peculiar was going on there, especially when he came to know after looking into the files of Alice Alquist's unsolved murder case that the gift of royal jewels of the victim was not recovered after her murder. Strongly suspecting about something wrong in the matter, Cameron decided to unofficially reopen the case and engaged an under-cover surveillance task to a policeman named Williams to watch Gregory, who they learn often visits an abandoned house nearby and is probably planning to institutionalize Paula.

As he became confirmed about Gregory’s intention, Cameron arrived at 9 Thornton Square in the evening, after Gregory had left the place to get into his house from the back to continue his search for the diamonds and offered Paula his help, gaining her confidence and trust by showing her one matching glove given to him by her aunt when he was an admiring, twelve year old boy. He confirmed that the attic noises and flickering gaslights are real and orchestrated by Gregory, who goes to the neighbouring vacant house to enter their own attic through a skylight. Paula has heard him searching through Alice's belongings, while the gaslights flicker when he turns on the attic lights, reducing the gas to the downstairs lamps. As Cameron opens Gregory's desk, Paula finds the letter from Bauer that Gregory insisted was a delusion and as Gregory Anton’s handwriting matches that of the letter, she became confirmed that actually Gregory is Sergis Bauer, who murdered Alice but somehow was interrupted before he could find her jewels. He married Paula only to gain access to her aunt’s property and carefully hatched a plan to drive her mad and have her institutionalized, leaving Alice's estate at his disposal and allowing him to peacefully search unabated for the jewels.

By that time, Sergis discovers the jewels in the attic, sewn into one of Alice's famous costumes. As he returns downstairs, he surprisingly finds his desk unlocked, when a mentally exhausted Paula replied that she did not do it and admits that she was visited by a man. But apprehending imminent danger for Paula, Brian Cameron appeared at the right moment on the scene and confronts Sergis, alias Gregory Anton, chasing him into the attic and tying him to a chair. With Gregory tightly bound in a chair by ropes and Paula is left alone with him, Gregory pleads her to make him free and tries to convince her of his innocence, Paula taunts him, wields a sharp knife in front of his face, musing that the knife in her hand might not be real. Before Constable Williams leads him away with his hands bound, Gregory explains the monstrous obsession that kept them apart. As the police drive Sergis away, Paula is consoled by Brian after her ordeal on the rooftop beneath a cloudy night sky, expressing interest in seeing Paula again and promising her to support, friendship and perhaps a hopeful future.

Released on 4 May 1944, Gaslight (1944) was critically acclaimed, a huge box office success and received seven nominations for the 17th Academy Awards. While Bergman's Oscar-winning performance for her stunning performance in the role of Paula Alquist has long been considered among the best to win Best Actress, Boyer's portrayal of Gregory Anton was also nominated. The film also earned a distinction in 2019, when it was selected for preservation as being culturally, historically or aesthetically significant, in the United States National Film Registry.