Dead Ringer is a 1964 film directed by Paul Henreid—yep, that Paul Henreid, the guy who played Victor Laszlo in Casablanca.
Edith Phillips (Bette Davis, Henreid's co-star in Now, Voyager and Deception) goes to the funeral of one Frank DeLorca. The man's widow, cloaked in mourning clothes, spots Edith and invites her to visit. It turns out that the widow is Edith's twin sister Margaret (Bette Davis, Acting for Two). Edith and Margaret haven't spoken since Margaret stole Frank away from Edith some 20 years ago. While Margaret has spent the last twenty years in the lap of luxury after landing super-rich Frank as a husband, Edith is barely getting by as the proprietor of a cocktail lounge. Really the only light in Edith's rather dreary existence is the presence of an adoring boyfriend, Jim (Karl Malden).
It soon becomes clear that while Margaret pretended she wanted to catch up with her long-estranged sister, what she really wanted was to rub Edith's face in Margaret's wealth. Edith is already in a bad mood when she finds out from a remark by one of the servants that Margaret lied about being pregnant 20 years ago. This news sends her into a boiling rage. After she gets back home she finds out that she is about to have her cocktail lounge foreclosed on for being three months late on the rent—and that might leave her homeless since she lives in an apartment above the bar.
A bitter, angry Edith takes drastic action. She invites Margaret to her apartment and, after Margaret shows up, shoots her in the head. She switches their clothes and assumes the identity of Margaret, stepping into Margaret's chauffered limo and riding back to Margaret's mansion. Naturally, things do not go smoothly.
This film is often said to be a remake of 1946 Bette Davis movie A Stolen Life, which featured a similar story about a Sibling Triangle and Impersonating the Evil Twin, but this movie was adapted from a short story called "La Otra". No connection to David Cronenberg film Dead Ringers.
- Always Identical Twins: The plot wouldn't work with fraternal twins, of course.
- Blackmail: After Tony sniffs out Edith as an impostor, Edith has to start handing over Margaret's jewelry. This backfires when Tony's attempt to sell valuable jewelry of dubious provenance attracts the attention of the police.
- Bluff the Impostor: Tony muses about how much fun he and "Margaret" had in various vacation spots. When Edith absentmindedly agrees, he nails her as an impostor. He was already suspicious and tested "Margaret" by mentioning vacation spots they'd never been to.
- "Could Have Avoided This!" Plot: Edith finds out far too late that after 20 years Frank still remembered her, and left her $50,000 in his will, which would have bailed Edith out of her financial jam.
- Dead Person Impersonation: Edith impersonates Margaret after murdering her. Ironically, except for Tony and Henry the butler, no one believes her when she confesses, and she's given the death penalty as Margaret.
- Evil-Detecting Dog: Inverted as Duke the dog, who hated Margaret, takes a shine to Edith. Possibly also played straight if one assumes that Duke was detecting evil Margaret murdering Frank.
- Evil Twin: Originally Margaret seems to be a low-grade bitchy version of this, as she stole Frank from Edith in the backstory and taunts Edith with her wealth after the funeral. Eventually it's revealed that Margaret really was an Evil Twin who murdered her husband.
- Foreshadowing: Among the plot points set up in the early going are that Edith smokes but Margaret doesn't, Duke the dog dislikes Margaret, and that Jim the boyfriend is a police detective. All of that pays off later on.
- Impersonating the Evil Twin: Edith murders her evil twin Margaret and assumes her identity, with disastrous consequences.
- Mrs. Robinson: Edith is unpleasantly surprised that Margaret had a lover much younger than she was, Tony the golf pro.
- Old Retainer: Henry the elderly butler. Eventually it's revealed that he figured out Edith's scam early on, but was willing to support her all the way to the end.
- Never Suicide: Edith shoots Margaret and makes it look like she, Edith, killed herself. Unlike how this trope usually plays out, the cops accept "Edith's" death as a suicide.
- Sibling Triangle: In the backstory. It seems that back During the War Edith and Frank fell in love in London. On a trip to Los Angeles Frank looked up Edith's sister, and Margaret ensnared him.
- Sympathetic Murderer: Downtrodden, lovelorn Edith is pretty sympathetic when she murders her Rich Bitch of a sister, and she becomes even more so when we find out that Margaret and Tony conspired to murder Frank.
- Widow's Weeds: Margaret wears a hat with a thick veil, which probably made the blocking easier in some of the Edith/Margaret scenes. Edith tells Margaret to take it off because she hates "fake mourning".