Thank God for Judi Dench.

As long as she is around, giving people a steely gaze and telling it like it is, whether as James Bond’s cantankerous boss in “Casino Royale” or as the “battle axe” of a schoolteacher she plays in “Notes on a Scandal,” there will always be films worth seeing.

Not that there aren’t other reasons to see “Notes on a Scandal.” Cate Blanchett and Bill Nighy (whom viewers might remember from “The Constant Gardener”) perform ably in lesser parts, and Philip Glass’ score puts you on edge like musical version of nails against a chalkboard. But without Dench, none of it would stick.

Dench plays Barbara Covett, who fills notebook after notebook with the unfiltered impressions of her keen and bitter psyche, and with all the charm of a steel fire door. In retrospect, this behavior hints at something much deeper than bitterness, but Patrick Marber’s (“Closer”) screenplay holds onto every detail until the moment of greatest effect. Thus, by the end, we are disturbed to find ourselves so well inside the mind of a borderline sociopath like Ms. Covett.

The story concerns the arrival of Blanchett’s Sheba Hart at the gritty London middle school where Covett chairs the history department. Hart is an instant school celebrity, more for her figure than for her teaching abilities. “Is she a sphinx, or merely stupid?” Dench’s character inquires with characteristic acidity in one of the narrative voice-overs that take regular—and usually shocking—extracts from her journal entries.

According to the movie’s tagline, “one woman’s mistake is another’s opportunity,” and Covett parlays Sheba’s guilt at being discovered making love to one of her students (catch the Biblical reference?) into what she believes is a romantic relationship. But when she discovers that Sheba and her student have kept up their affair, her delicately constructed self-delusion collapses, or rather explodes, taking everyone nearby with it.

Director Richard Eyre has an eye for thorny romance: his last film, 2004’s “Stage Beauty,” wrapped Claire Danes and Billy Crudup in questions of gender identity and theatricality in the dying days of male monopoly on the English stage. This story is more conventional, rather like “American Beauty” meets “Blackboard Jungle,” but Eyre succeeds in keeping the film engaging where it could have felt stale.

“Notes on a Scandal” is up for four Oscars—Dench for Best Actress, Blanchett for Best Supporting Actress, Best Original Score, and Best Adapted Screenplay. As good as Dench’s performance is, her odds of winning are anemic, given that Helen Mirren has scooped up the honors at every main awards show this season. It has a shot at the others, but regardless of Oscar success, Dame Judi earns a gold star in my book.

—Staff writer Jillian J. Goodman can be reached at jjgoodm@fas.harvard.edu.