Movie opens with frazzled yet pretty woman in her late 30s/early 40s talking in a police about an accident. She explains how it was dark and she was distracted and lost control of her car on the wet pavement and ran over a young woman she didn't even see. Her husband (Aidan) is outside the room, speaking with another officer. The woman (Daphne) is released, couple reunited with an emotional hug, and the lead detective chats a bit with the husband alone. the husband says, "It's just a shock for me since she's been driving since she was 16". The cops back at the station discuss the case being an accident involving a well to do couple, and whoosh this gets filed an accident, no charges. Wrap it up late on a Friday night, it's a weekend.
The lead detective (Rick) goes home, sleeps, wakes up, and then flips through the driver's file. Something feels off. He drives to state records house (great movie fake place) and sees her license was first in the late '20s and with no state transfer. She's been driving less than 5 years; not since she was 16. It irks him, and he wants to check in on her and husband, so he drives to their place. Couple (Aidan + Daphne) live in well kept place off the road, gravel driveway, large lot in Sudbury. The husband entertains him with an offer of alcohol or tea. Butler serves them. He has a cup, goes to smoke, and he asks him not to. They don't smoke and blame asthma. Rick the cop asks husband how wife is. Husband says she's resting. Wife comes down, looking tired. Cop peppers them with questions about their home, how they met (college, cop squints looking puzzled), their wealth (made it in the crash, bet the other way on the market), and asks the husband about the driving since she was 16 remark. Wife interrupts and says, it must have been 26. Aidan blames emotions and confusion for his comment. Wife mentions needing to rest, ending the conversation. She makes a move and reveals some skin, showing a tattoo at the base of the spine. Wife invites cop to a party the next weekend.
Cop spends week asking around about couple. Few in area know of them, so he must look by other means. Employment records start in early '20s. Finds no education records of them attending college. So they're liars about their pedigree, big whup. Finds out they had moved to Boston/Lowell and worked in the mills through the '20s. Thru it all, they always had a stockbroker. Cop visits broker. They always picked right, and would brush aside recommendations from him. He even started buying alongside their market bets. They accumulated enough wealth for major short in '29/30. Huge payday, cash out and set up shop on an estate in an in old Colonial in Sudbury. Patron of arts, throw great parties, and has a tight circle of friends. Broker suspects they use reefer. Cop asks broker about tattoo on wife. Broker says yes, Daphne's tattooed in odd places.
Aidan shows up at police station. Chats up Rick about the accident. Reveals he knew the victim. He had an affair with her. It had ended a while ago but she had approached him again recently, but he denied her. He wanted to come clean about it as he felt guilty and wanted to hide it from his wife when the cop visited the weekend before. Odd coincidence how things worked out. Two women he loved brought together in an intense moment.
Cop now feels disgusted by this lying yet charming man. Rick reads over the interview with the victim's mother. Sees line, "She went out to wait for a friend to pick her up out front". The accidental death by your fling's wife looks too coincidental now. Rick assumes the husband must've set something up that the wife got wind of, but he checks the log for when they called the husband. Sure enough, he was home and answered as the only person in Sudbury with a direct line. How did Daphne know but Aidan didn't go? Cop goes to see victim's mom.
Victim's mom has photos of her up. Mother discusses how her daughter wanted to go to college after being filled with ideas by her friend. Rick assumes Aidan, but mother says, some spinster talking flapper nonsense. Rick asks for a name, and she says Daphne. He asked her if she was picking her up, but she says she never heard the woman's voice only knew the name. Asked if her daughter dated. Mother says boys here and there, but she had been quiet the last year. Focused on work, the library, going to museums.
Rick attends Aidan and Daphne's dinner party. He meets a few friends who all are of the genteel crowd and have a similar look. He goes to smoke at the party, and gets the stink eye. One fellow says that he'll join Rick on the balcony for a smoke. He drops how it's bad for you. Rick says, "What are you talking about? Smoking relaxes him and tastes great." They eat a great meal, where Daphne overly describes all of the food. They drink alcohol and when drunk, another woman complains about the music. She didn't think the music would be so boring with everything she had read. Rick is confused, as they are listening to newer, different stuff. He asks about children, but no one there has any. Eventually, some flirty gal makes the moves on him and they get down in the house. Even though she keeps her clothes on (for the censors) he sees a tattoo on her. She's drunk and afterwards, he asks her what is she thinking, and she says, "My husband and I didn't realize monogamy would be this hard".
As the party winds down, Rick asks Daphne about meeting Aidan. She recounts a tale of seeing him at college. Nice yarn of connecting, breaking up and then reconnecting. Rick drops it on her, "That's a good lie, you tell it so convincingly, you never went to college. You knew that girl you ran over, wanna lie about that, too.". Aidan grabs Daphne and whisks her to bed. He then has the butler escort Rick out. Rick then prepares to approach them again on Monday. He spends the day on Monday looking up the woman he had sex with. She and her husband, like Aidan and Daphne, are a couple who came into money in the late '20s. No real records of them before early '20s, minor employment with land speculation gains in Florida. They sold out just in time. Wife has similar tastes as Daphne. They are a near mirror of each other's likes and dislikes. Rick is going to confront Aidan and Daphne.
Rick drives to Aidan and Daphne's house at night. No butler. Aidan lets him in. Rick goes straight at him about victim and Daphne. Your wife knew, blah blah blah. Aidan says it wasn't like that. It was an accident. Daphne starts screaming at him from the stairs. Mentions breaking the rules. Aidan denies breaking rules, but she says "our rules not the rules". She launches into how Aidan, Daphne and victim had engaged in threesome sex. Rick is pretty stunned. Aidan had not cheated on Daphne initially. Daphne had continued an affair with victim after Aidan broke it off with girl. Girl rejected Daphne, and then Aidan had interacted with victim again. He broke their marriage rules. Rick stops them and says, "you're both going downtown because you're lying about everything and there's a dead girl you two are fighting over".
Aidan sits in chair and says, "We can't do that". He then launches into what the rules are. Daphne grabs firepoker from fireplace. Starts yelling at him to shut up. Rick calms her down but she still has firepoker in her hand. Aidan then explains how he didn't break any rules. The victim was fair game for sexual play. She was also fair game in the relocation rules. Aidan explains how Daphne and he are from the future. They are from an era with plenty of dysfunction, gloom and doom. No one can figure out how to go forward in time, but they know how to go back. Resources are constrained and to keep a high enough standard of living for a nice layer of the upper 20% and to prevent the other 80% from overrunning them, they send people to the past of their choosing to live quiet lives of comfort. Rigorous testing and usually just singles, but couples can go with more rules to follow. If rules are broken consistently, a follow up unit is sent. Aidan and Daphne chose to go back to 1922 to live after age 30.
"Why doesn't anyone go back to fix things?" Aidan answers, "First adopters tried, but failed miserably as things just remained the same no matter who went back and when. They gave up. Maybe because those on top in our time wouldn't be on top, and it is a huge step for someone to voluntarily relinquish power". "Isn't that what you did?" Aidan answers, "No, we were on the edge, smart, and didn't want kids. That's a rule, must be sterilized to relocate, plus we revered the beauty of the past."
Daphne also explains how she loves this time but misses some freedoms of her time. A person is always a product of their home. 1930s Massachusetts isn't home. It's a museum. They can't make friends. They can't interact. They can't seek new things. The victim was a chance to do that. Aidan had told her to stop, she knew she had to stop. She set up meeting, but knew she had already changed the victim. Had to kill her. The girl's last name was nothing to Aidan and Daphne. What's one poor rural girl dead going to change? Aidan rises and tells him there are others, now, before and in the future. They'll stick to themselves. When Aidan and Daphne die, they will leave a note in a will with instructions for the relocation organization to refine the process.
Rick goes to the door and turns back. Speaks to Daphne with firepoker still in hand, "She may have been mother of the man to fix things". The couple laughs. Rick realizes that this couple has no remorse. Their fatalism and belief in predestination is so complete that he needs to shock them. He smiles, and tosses a gun to Aidan. Aidan catches it and Rick shoots him in the head. Daphne is screaming at them with the poker waving in her arms. He shoots her in the chest. As she lies on the floor dying, he leans down and says, "I will find you all, and prevent you from playing with us like pieces in a gallery." He walks over to their ornate phone and rings in the precinct. Starts out with, "Hello, send the meat wagon, you're not going to believe this one...".