A honeymoon goes dreadfully wrong but the film that details the deterioration turns out very well. Dominic Cooke’s “On Chesil Beach,” adapted from his own novella by Ian McEwan, is an elegant but heartbreaking tale of a love affair that blossoms at a time of sexual repression—the early 1960s—and collapses in recrimination after a wedding that delivers pain rather than joy. Some readers of the book will argue that McEwan miscalculates at the close, adding a contemporary postscript that they interpret as a sentimental concession to the expectations of filmgoers (as opposed to readers, who are accustomed to harsher realities). But there is no denying the emotional satisfaction of the ending he has chosen.

The newlyweds in question are Florence Ponting (Saoirse Ronan) and Edward Mayhew (Billy Howle). Both are recent university graduates, she in music and he in history, but they come from very different backgrounds. Her family is upper middle class, her father Geoffrey (Samuel West) a brusque factory owner and her mother Violet (Emily Watson) a haughty, opinionated academic; there is also a younger daughter, Ruth (Bebe Cave). They live in a well-appointed house in the city.

By contrast, Edward hails from a troubled rural family. His father Lionel (Adrian Scarborough) is a teacher in a public school who cycles to work each day, and his mother Marjorie (Anne-Marie Duff) suffers from brain damage caused by a long-ago accident. Their household is a perpetual mess, and Edward’s younger twin sisters Anne and Harriet (Anna and Mila Burgess) are often left to fend for themselves, while all are devoted to caring for Marjorie, who is susceptible to shedding her clothes out in the garden.

Florence and Edward meet at a lecture on nuclear disarmament and quickly become friends, and the friendship grows into romance. It is, however, a restrained and decorous one, governed by the rules of the day. Both are sexually inexperienced, Florence more so than Edward; she is a virgin, one whose fear of disappointing him—not to mention her own ambivalence–are profound.

Thus the nervousness as the couple sits down for dinner served by two rough-and-ready waiters in the room of the shabbily genteel hotel on the Dover coast that serves as their honeymoon suite. They manage to get through the meal, but when they repair to the nearby bed, disaster strikes. A long, difficult conversation that follows on the beach proves even more disastrous.

That is the essence of the film, played out with a deliberation that is often cringe inducing—not because the writing is poor (in fact, it’s brilliant), or the direction misguided (in fact, Cooke shows extraordinary skill in dramatizing the action), or Nick Fenton’s editing dilatory (it helps to create a mood in which things are almost always held back), but because the decisions taken by the characters are so painfully etched. And the acting is remarkable, from the beautifully calibrated supporting work by Watson, Duff and Scarborough (only West veers toward caricature), but especially by the leads. Ronan, as she has so often been, is amazing, and she’s matched by Howle; together they succeed in conveying, through their gestures as well as the dialogue, the inner turmoil of the characters that McEwan could reveal by access to their thoughts in the book.

There is, moreover, a dimension to the story that the film can provide more effectively than its source did: the music to which Florence is so devoted (Edward’s tastes run more to jazz and rock). She is a violinist, in fact the first violin in a string quartet (sometimes augmented to perform quintets), and here one can hear their playing rather than merely being informed of its effect. That’s an important aspect of what becomes the group’s signature piece—Mozart’s D Major Quintet (K. 593), with its achingly gorgeous opening (described by Florence as a question-and-answer, reflective of the story’s theme). But it’s also good to hear the first movement of the “Haffner” Symphony rather than just having it described; and other snippets by Mozart, Bach, Haydn, Beethoven, Schubert and Rachmaninoff add to the emotional texture of the scenes they accompany. They all dovetail well with Dan Jones’s original score.

The film looks impeccable as well, with Suzie Davies’ production design and Keith Madden’s costumes creating a convincing period effect and Sean Bobbitt’s widescreen cinematography using the play of light for maximum impact in both the interior and exterior sequences, the latter shot on magnificent locations.

Be forewarned that “On Chesil Beach” is not a date movie, despite the radiance of Ronan and Howle. Or perhaps it might be, providing as it does a salutary warning against the dangers of over-expectation. Of course, in this far more permissive day and age its characters might seem almost incomprehensibly reserved, but as a portrait of past reality—especially of the British sort—it’s exquisitely rendered.