The clues add up in this cute and vulgar British whodunit.

“Wicked Little Letters” tells the story of a devout Christian woman in Littlehampton, England 1920s, who keeps getting harassing letters, and accuses her Irish next door neighbor of writing them, because of her potty mouth and dirty mannerisms. And many more people have been receiving these disgusting letters. The movie informs us that this is based on a true scandal, and that the story has recently been discovered.

Even if certain elements don’t make sense, there’s a lot of good motives to the case. The devout Christian woman is Edith Swan (Olivia Colman), whose father Edward (Timothy Spall) is demanding enough to make her meek in front of him, and the accused is Rose Gooding (Jessie Buckley), who is dating the guitarist Bill (Malachi Kirby) while raising her little girl from a previous marriage (Alisha Weir from “Matilda the Musical” and the upcoming “Abigail”). She refuses to apologize for standing up to Edward at his party, and she does accuse Edith of calling social services on her. As a matter of fact, given the time period and location, you know how people are against cursing and vulgarity.

What I’m really amazed is that Rose can curse in front of her child, but usually scolds her for playing her boyfriend’s guitar, because “good girls don’t play guitar.” Now, this would seem typical, and I am a guy who loved defending women regardless of the time periods, but these scenes are the least of Rose’s worries.

You’re able to see the levity and seriousness within Colman, Buckley, and Spall, regarding the right kind of themes. And you’re also interested in how this true story played out, and you’re also rooting for Rose to be innocent. Just because people say and do things differently than normal people, doesn’t mean they’re bad people. It’s about proving misunderstood people have their hearts in the right places.

There’s also the woman police officer Gladys Moss (Anjana Vasan). Yes, a woman police officer. She wants to get involved with the case, but the men Constable Paperwick (Hugh Skinner) and Chief Spedding (Paul Chahidi) both inform her: “Women officers don’t sleuth.” And apparently, they’re not supposed to have children. I thought that was for nuns. But I don’t know everything, so please don’t insult me. What I like about this character is the way she keeps a straight face with her big eyes merging with her personality. I’ve never heard of Vasan before, but she does a good job here.

But anyway, Moss knows Rose is innocent, based on the handwriting, and enlists some help from Edith’s friend group-Ann (Joanna Scanlan), Mabel (Eileen Atkins), and Kate (Lolly Adefope)-to get to the bottom of this. They’re the kind of characters I looked for and missed in “The Miracle Club” with their honest whimsey.

“Wicked Little Letters” was directed by Thea Sharrock( “Me Before You,” “The One and Only Ivan”) and written by Jonny Sweet (“Comedy Showcase,” “Chickens”), who both seem to enjoy making a British comedy that knows cursing and likable characters when it sees them. Unlike certain raunchy American comedies, this period comedy doesn’t force the cursing on the characters; it allows them to acknowledge how certain people would use them within their behaviors. And it features certain kind of vulnerabilities and emotions within them, as if the movie was following in the tradition of Martin McDonagh’s work.

So, if we look past some of the cynicism within the screenplay, we can see the outspoken and courage spirits that women have in this world. We’ve always known that, but when subjects like this appear in movies, we still want to support them. And it works well in this whodunit or “Who Wrote It,” as the promotions would suggest. Makes more f***ing sense, doesn’t it. Pardon my French.