Plot

When people in Littlehampton--including conservative local, Edith--begin receiving letters full of hilarious profanities, the rowdy, Irish migrant, Rose, is charged with the crime. Suspecting that something is amiss, the town's women investigate.

A 1920s English seaside town bears witness to a dark, absurd scandal in this riotous mystery comedy. Based on a stranger-than-fiction true story, "Wicked Little Letters" follows two neighbours: deeply religious local Edith Swan (Olivia Colman) and rowdy Irish migrant Rose Gooding (Jessie Buckley). When Edith and fellow residents start to receive wicked letters full of unintentionally hilarious profanities, foul-mouthed Rose is charged with the crime. The anonymous letters prompt a national uproar, and a trial ensues. However, as the town's women, led by Police Officer Gladys Moss (Anjana Vasan), begin to investigate the crime themselves, they suspect that something is amiss and Rose might not be the culprit after all.—STUDIOCANAL

England, shortly after World War 1. Townsfolk in the small town of Littlehampton have been receiving disturbing, profanity-filled letters. Suspicion immediately falls on the drunken, foul-mouthed Irishwoman Rose Gooding. Her neighbour, the extremely conservative and pious Edith Swan, has Ms Gooding arrested.—grantss

The film begins in Littlehampton, with the 19th crude letter, addressed to Edith Swann and she and her family sit round the kitchen table and Edith says that she is convinced that it is her neighbour, Rose Goodings. This makes her father angry and he marches up the seaside and into the police station and gets the constable to come and have a look at the letters.

Meanwhile, Rose tells her daughter Nancy not to play the guitar, before she leaves her with Bill and goes to the pub. Nancy immediately goes to play the guitar when she leaves.

After reading all the letters and hearing the stories, the constable goes to the pub, where Rose is playing darts and arrests her. When she gets to the station, Rose sees Woman Police Officer Gladys Moss, before getting thrown in jail. Later, Edith tells the police officers the story about how Rose came to Littlehampton from Ireland, after her husband died in the war and started off as Ediths cleaner, but soon became friends, until Edith's father irritates Rose, at his birthday party and she storms out in anger and Edith says the letters started just after that.

Later in the trial, Rose is sent to Portsmouth Prison for 2 and a half months and she tells her family that it is probably alright, but the prison turns out to be worse than the first. Whilst in prison, Rose wrote Gladys letters trying to prove her innocence and get help, but as a police officer, she couldn't help her. Gladys does however notice that Roses handwriting is different to the letter writer and she tries explaining that to the chief of police, but he still believes it was Rose.

Gladys pushes her bike to Edith's house and Edith tells Gladys that she really does believe it was Rose who wrote them and the fact that her religion prevents her from lying. Edith and Gladys go to her Woman's Wiste and discuss that they believe Rose is guilty. Later though, two of the women get Rose out for bail until the trial for £3.00, with one of them selling a sick pig.

Rose gets home and tells Nancy off for playing the guitar, before going for a bath and a smoke. After turning away the press, Bill answers the door to Edith's angry dad, who is holding a letter in his hand and he and Bill start fighting, before another woman came along and announced that she has also received a rude letter and soon, the letters spread across the county and the police start panicking over Rose, but Gladys is still skeptical. While Rose was doing laundry, Edith came up to her and says she forgives her and the father is there to read a passage, but Rose rejects. Rose came over to Gladys' house and Winnie, Gladys' niece answers the door and Gladys rejects letting Rose in at first, but eventually gives in and lets her in, to get more information. Back at the Swann household, Edith's father tells her to go to her room and write out proverbs 11-12 200 times, which she does. After she finishes however, she opens a hole in the wall and gets out a book of naughty letters, before writing another one out, revealing Edith as the mystery writer and posts it through the front door. Edith's mother reads the letter and has a heart attack and Edith throws the letter in the fire, before going to get help, but is unfortunately too late.

Gladys comes round Edith's house to confirm the body and Edith signs a waiver and Gladys notices that the "G" on the waiver is exactly the same as the ones on the letters and she tries telling the chief that Edith is guilty, but she gets suspended for asking questions behind his back and says she can have the handcuffs, but if she was caught again, she'd be in them. Now off the force, Gladys and another woman from the wist group follow Edith as she posts more and more letters.

The day of Roses trial arrives and Rose answers all her questions honestly and the defendant asks Edith to read a letter, but she refuses. After, they analyze Roses "G" and Edith's "G" and it is announced that Edith's is the replica of the "Gs" in the letters, but Edith just acts more innocent and says that god will see who is guilty, before Rose is asked about her husband and she doesn't answer and Bill and Nancy run out. The trial is put on pause. That evening, Rose tells Bill about how she left her former husband for Nancy and Bill runs off, before Nancy runs out in anger and attempts to break the guitar. Bill comes back the next morning however, and gives Rose a cup of tea as she wakes up, just as the police arrive and she runs away and the police follow her down town.

Gladys measures Winnie's head, before looking in her father, who was also a police officers case and sees an empty bottle and develops an idea. Gladys meets up with the women from Wiste and tells them her plan to prove Edith guilty, but not before one of them has her egg. The group use ingredients to make invisible inc and go undercover to prove Edith guilty. When Edith goes to get her stamps, they give her very specific stamps and she writes one more letter aimed at the judge, before Rose comes and asks Edith why she is constantly using the same words, before teaching her how to swear properly. Edith posts the letter, thinking she got away with it, until it is revealed that Winnie was inside the postbox and Gladys gets it out, in front of the other police officers and uses the invisible inc on the letter and Gladys arrests Edith, using the handcuffs and Rose is proved innocent in court, before Edith goes by, joking about writing to her in prison.

Rose tells Nancy to close her eyes and gives her, her very own guitar and Edith gets thrown in the back of the police carriage and Edith's father doesn't believe it was his daughter who wrote the letters and Edith tells him she will never see him again, before swearing at him and laughing as she was taken off to prison.