As her marriage flounders to college professor Jack Maye (Stanley Tucci), eminent High Court judge Fiona Maye (Emma Thompson) has a life-changing decision to make at work - should she force a teenage boy, Adam (Fionn Whitehead), to have the blood transfusion that will save his life? Her unorthodox visit to his hospital bedside has a profound impact on them both, stirring strong new emotions in the boy and long-buried feelings in her.

Ian McEwan's work is often marked by taking time as a central concept and playing with it over the course of the story. 'Atonement' was set over several time periods, each interweaving with the other to create a full tapestry. 'On Chesil Beach', meanwhile, locked it into a firm twenty-four hour period. 'The Children Act', however, has no such flourishes to it, but it still draws heavily on themes that McEwan has explored before - namely, the end of love, the muddiness of human relationships, and all of it wrapped up in far too eloquent sentences and monologues.

The movie opens with Emma Thompson, hunkered over a laptop, furiously battling away at a keyboard as she works through the night on yet another high-profile case. Her husband, Stanley Tucci, rolls into their desperately bourgeoisieapartment and proudly proclaims that he's intending to have an affair and she can either like it or lump it. From this, an entire movie could have been spun off and the dynamics alone are fascinating enough to sustain it, but instead, it quickly shifts gears and moves into a high-wire legal drama about a Jehovah's Witness family who have a deathly ill son, played by 'Dunkirk' breakout star Fionn Whitehead. That Thompson is able to navigate both of these conflicting stories with relative ease speaks to her abilities as one of the strongest female acting talents working today, and in the hands of anyone else, it would have failed.

Director Richard Eyre skillfully places Thompson front and centre throughout the story, and her solitary nature is shown with real subtlety and nuance that it's so slight in its execution, but has a devastating impact. She's become so cut off from everything around her that she can't even allow herself to feel anything until it's far too late. Stanley Tucci, it must be said, is under-utilised, but this is only because he's so absent from her life that if even he was in every scene, Thompson's character would be ignoring him. Fionn Whitehead plays up the wide-eyed teenager a little bit too earnestly, but his on-screen parents - Ben Chaplin, in particular - more than make up for it.

So much of 'The Children Act' plays out in small scenes with minute, understated performances. It's a very adult movie, not in terms of explicitness or the like, but in the sense it's adults coping with life and relationships in a very grown-up way. Thompson doesn't have a public breakdown, she's snapping at work colleagues in a way that anyone's who been through a break-up would. She doesn't run to her husband's office to confront him, but instead she waits for him to make the first move. It's all done in such a convincing, relatable way that the level of emotional intimacy can be devastating, and it's all done in such a mannered and controlled environment that it heightens the intensity.

While the final act derails the story and never really gets itself back on track, there's more than enough to 'The Children Act' for it to be worth your time.