Modern classics don’t come along very often. “Consent” is, without a shadow of a doubt, just that: an intricately constructed philosophical drama that does for love, law and language and what Michael Frayn’s “Copenhagen” did for particle physics and Tom Stoppard’s “Arcadia” did with time. The play, premiering at London’s National Theater, makes grand abstract ideas both human and theatrical and, in one shot, elevates its writer Nina Raine, whose last play “Tribes” was a transatlantic hit, into the major league of British playwrights.

“Consent” reflects off a contentious rape case. A working class woman alleges she was raped on the night of her sister’s funeral. The accused claims she consented. What feels cut-and-dry to the victim is, legally, if not morally, much murkier. A case that’s already clouded by circumstance is further obscured by legalese as the victim gets bamboozled by the defense lawyers.

As well as picking at the injustices of the legal process (the victim’s history of depression works against her, but the accused’s previous conviction gets excluded), Raine raises the impossible notion of a rape without a rapist. The victim’s adamant she didn’t consent; the accused is convinced she did. This isn’t just one word against another. It’s two separate and irreconcilable truths. Feelings bear no relation to fact.

Those ideas linger in the air as “Consent” moves elsewhere. Its main thrust concerns the private lives of the lawyers involved: barrister Edward (Ben Chaplin), acting for the defense, and his wife Kitty (Anna Maxwell Martin) are friends with the case’s crown prosecutor Tim (Pip Carter). When they try to set him up with an actress friend Zara (Daisy Haggard), who’s up for a big legal drama herself, their own marriage comes under strain.

Having counseled their best friends Jake and Rachel (Adam James, the most affable adulterer, and stern and sympathetic Priyanga Burford), also lawyers, through their own rocky patch, Edward and Kitty find themselves in a similar situation. Fraying under the pressures of motherhood, never having forgiven Edward over a previous indiscretion, Kitty winds up in an affair of her own. After a fraught argument, she accuses him of rape.

“Consent” is a watchmaker’s play, full of tiny moving parts. The whole thing pings with questions of consent — not just sexual but personal: set-ups, sacrifices and unforeseen consequences. Everything’s going on behind somebody’s back. No one ever has the full picture. And yet, everyone’s judging everyone else. Throughout, Raine maps the legal process onto everyday — the laws of love, as it were — so that couples enter disputes, while friends advocate and adjudicate. Everyone is, at all times, an interested party. No one’s dispassionate.

It’s why the play throbs with performative language: Words don’t just describe the world, they affect it. To speak is to act. Just as a declaration of consent alters a sexual encounter, so Raine’s characters talk one another into bed, even into love and forgiveness. The same’s true of the law: rewrite it and you reorder the world. Text messages betray infidelities and off-hand comments leave lasting wounds. In court, meanwhile, questions aren’t just questions. They accuse, they confuse, they answer themselves. Words, Raine makes clear, have power. That’s as personal as it is political. Well-spoken lawyers run the world. Can any of us consent to the law?

Really, underneath, it’s a play about relativism, and Raine shows how our moral judgements shift according to our situations, as feelings intrude and alter the facts. In one confrontation, she gives Kitty a toothache, just to complicate proceedings. She shows how people change. Edward’s cool logic deserts him as the play goes on. Zara, eventually, falls for Tim. Feelings slip and slide. Lawyers are lovers and vice versa. Their actions and assessments differ accordingly.

Nothing in “Consent” is stable or fixed. It’s a point Raine makes brilliantly, with humor, as the lawyers’ mordant jokes about their clients cut very close to the bone. Whether rape jokes are funny or flatly offensive depends entirely on your point of view. They are, of course, both.

The real brilliance of “Consent,” then, is structural, and her characters all come full circle. Her plot forces the shoe onto the other foot, so that cuckolds get cuckolded and judges get judged. It adds up to a forceful case for empathy.

That gets to why the play works so well. It chimes perfectly with its medium. Theater’s sometimes called an empathy machine. More than any art-form, it deals in doubles — actors and characters, stage and setting. It holds its own contradictions. It turns words into action. Raine’s play does the lot and Roger Michell’s minimal production instills an artful permeability to the event.

Hildegard Bechtler’s design casts the play in shades of grey on a slab of stage between two banks of audience. Domestic lights drop down to signify locations and the furniture seems to rearrange itself between scenes, a neat and disorientating embodiment of the relativity at the play’s heart.

Heart might be the one thing “Consent” is lacking. It’s so stuffed with ideas and so intricately constructed that it can feel calculated, despite some rich performances. Chaplin falls apart superbly as Edward’s pain cracks his cool rationality in half, and Maxwell Martin lets frustration accumulate into frayed edges. It is, in the end, the play that dazzles: dizzyingly intelligent and beautifully judged.

London Theater Review: ‘Consent’ by Nina Raine

National Theatre, London; 400 seats; £55 ($68) top. Opened, reviewed April 4, 2017. Running time: <strong>2 HOURS, 20 MIN.</strong>

  • Production: A National Theatre and Out of Joint co-production of a play in two acts by Nina Raine.
  • Crew: Directed by Roger Michell. Set design, Hildegard Bechtler; costume design, Dinah Collin; lighting, Rick Fisher; music, Kate Whitely; sound, John Leonard; dialect coach, Charmian Hoare; legal adviser, Jessica Jones.
  • Cast: Priyanga Burford, Pip Carter, Ben Chaplin, Heather Craney, Daisy Haggard, Adam James, Anna Maxwell Martin.