Alexander Wilson lived an improbable, deceitful, destructive but undeniably intriguing life. An author of popular spy novels and a British secret agent himself in World War II, he married four women from the 1920s through the ’50s without bothering to divorce any of them. He managed to keep his four families mostly secret from each other during his lifetime, and his children (and many grandchildren) only got to know one another more than 40 years after he died.

Sounds like a movie. And it is, or in any case a three-part BBC mini-series, which begins Sunday on PBS’s “Masterpiece.” But Alexander Wilson, better known as Alec, isn’t the main character in the show, which is called “Mrs. Wilson” and takes place mostly after his death in 1963.

That’s what happens when you devote your life to secrecy and, despite publishing 27 books, never tell your own story. But mainly that’s what happens when one of your curious grandchildren turns out to be a famous actress. Ruth Wilson of “Luther” and “The Affair” is the granddaughter of Alec’s third wife, Alison, and she plays her victimized, mystified grandmother in “Mrs. Wilson,” of which she’s also an executive producer.

So rather than the historical adventure or romance it might have been in an earlier era, “Mrs. Wilson” is an interrogation of history, a feminist critique of mid-20th-century British society, a mystery and, least satisfyingly, a character study. The strangeness of the story, and Ruth Wilson’s characteristic intensity, pull us along. But Alison and Alec, and their motivations, never seem to come completely into focus. The series feels caught between fiction and real life, as if the writer (Anna Symon) and the director (Richard Laxton) were unwilling to fully dramatize a history that’s still murky, partly hidden in the files of the British Foreign Office.