I have to start this review by revealing that, because my wife is a fan of Sherlock Holmes stories, we have watched several movies and TV shows about the famous detective and his curious cases. Unlike her, I don’t have the kind of mind that can unravel mysteries, so the denser the plots became, the more bored I got. That feeling started creeping over me again while watching “Enola Holmes,” which introduces us to the previously-unknown 16-year-old sister of Sherlock (Henry Cavill) and his older brother, Mycroft (Sam Claflin).

As the movie begins, Enola (Millie Bobby Brown from “Stranger Things”) lives at home with her mother, Eudoria (Helena Bonham Carter), who has been home-schooling her daughter in a non-traditional curriculum that includes fighting and self-defense, deciphering and solving puzzles, and observing the world with the same kind of keen eye as her brothers. When Eudoria goes missing suddenly one day, the older Holmeses return to handle the younger sibling they haven’t seen in years. Mycroft claims that, as the oldest, Enola is his ward, and wants to send her off to a finishing school that the teenager has no interest in.

Meanwhile, there’s another plot line involving young Lord Tewkesbury (Louis Partridge, who my wife described this way: “Very pretty, that boy”), whose situation Enola becomes entangled in when she travels to London to solve her mother’s disappearance. From there, I can’t explain any more of the plot because I stopped caring. So, I’ll get to the performances instead.

Brown is as likable as you’d want any leading character to be. I liked the way she broke the fourth wall, although that conceit was used far too much in the last half hour of the movie. The way Claflin plays Mycroft, he can only be described as a dick. As for Cavill, who was positively bland in two big-budget projects of the last decade (“Man Of Steel” and “The Man From UNCLE”), he injects Sherlock with absolutely no personality at all. Benedict Cumberbatch played that role so much better in the BBC series. Fiona Shaw (“Killing Eve”) shows up as the woman who runs the finishing school, as cliched a character as in every British drama since “Oliver Twist.”

Aside from Brown, the only one who acquits herself well in “Enola Holmes” is Helena Bonham Carter as Eudoria. I can’t think of more than one or two other films in which I’ve enjoyed Carter’s work (maybe “Ocean’s 8”), but her presence in the early scenes — and too many flashbacks — with Brown are the highlights.

Oh, and don’t even get me going on yet another example of the dreaded dead-not-dead banality that writer Jack Thorne and director Harry Bradbeer rely on during what is supposed to be an especially tense moment. That old trope should be declared off-limits for all future screenplays, right up there with “There is no way I’m going with you,” followed by a smash cut to whoever said that going with whoever they said it to. There should be a financial penalty for such lazy writing.

It seems clear that “Enola Holmes” is meant to launch a new movie franchise — based on a series of novels by Nancy Springer —  and there’s nothing wrong with that, particularly with a fresh-faced talent like Millie Bobby Brown in the lead. Unfortunately, this first chapter didn’t even keep my Holmes-loving wife interested all the way through.

I give “Enola Holmes” a 4 out of 10.