As a thoughtful judge in ‘The Children Act,’ Emma Thompson rules

What follows is in all other ways a review of the film “The Children Act,” but let’s take a moment here at the start to lavish praise on Emma Thompson.

Thompson is, of course, an Oscar-winning actor, an Oscar-winning writer and a delightful presence in everything in which she appears. The films she’s in aren’t always as good as she is, especially lately. Here, playing a London judge named Fiona May, she gets a choice role in a somewhat uneven film — but her performance is so good that she overwhelms the story’s shortcomings.

Ian McEwan (“Atonement”) adapts his novel for the screen; Richard Eyre directs. They establish Fiona as a no-nonsense jurist who is forthright in her decisions, carefully considered and strongly stated.

We understand from the beginning that Fiona works a lot; her husband, Jack (Stanley Tucci), a classics professor, announces that he would like to have an affair.

Nothing against Fiona, you understand. He just feels neglected, so this appears to be his best option for any sort of intimacy. (He’s already picked out a partner. It’s not clear at this point if she is aware of her part in the negotiation.)

While she’s somewhat taken aback by this, Fiona is also busy. Cases to hear, decisions to make. She coolly works out how a pair of conjoined twins will be separated, even though it will almost certainly mean the death of one of them. But the law is the law.

So here we have a judge deciding the fate of other families when she can’t work out the problems of her own. Subtlety is not one of the film’s strong suits.

But that suits Thompson just fine.

The next high-profile case arrives swiftly. Adam (Fionn Whitehead) is the children of Jehovah’s Witnesses, almost 18 but not quite. He has leukemia that will kill him without a blood transfusion — one that neither he nor his parents want for him, but that will likely save his life all the same.

Fiona hears the testimony of doctors and scientists and of Adam’s father (Ben Chaplin). Then she takes an unusual step: She visits Adam in the hospital, where he lies, dying. He’s precocious and forthright and determined to refuse the transfusion. In the meantime he has learned the guitar and accompanies Fiona in a song.

It’s all very British and high-minded and, ultimately, a ruse: The law is the law, so of course she will order the transfusion.

This is hardly a spoiler; the movie depends on what happens after Fiona’s decision. Rarely in a film do we go past whatever makes the headlines. Here we see the effects on Adam’s life — and the effects that life has on his family. He lives. Now what? What does that mean, and how does it play out?

Fiona will remain aware of Adam’s life, unable to leave behind this case once the headlines fade. His role in her life is both a weak point in the narrative and essential to its progression. In the meantime Fiona must deal with Jack and the state of her marriage, perilous as it may be.

And she’s practicing her piano for the Christmas party.

Admittedly, stacked up like that, this sounds almost silly, but “The Children Act” is not at all a workplace comedy about a Type A judge struggling to balance home and work life.

McEwan, as is his wont, aims for something bigger here, the bigger questions — the biggest, even, of life and death. Thanks to Thompson’s outstanding performance, he mostly achieves what he sets out for.

‘The Children Act’

★★★