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Not many movies contemplate the importance of rage. They do not contemplate rage at death, the callous chaos of the universe, ourselves and those around us. A Monster Calls was written by Patrick Ness, and is based on his award winning children’s book. So it does its duty in making you reach for the tissues. But it includes, well, a monster. So it gives that darker emotion its due.

Conor O’Malley (Lewis McDougall) is a young teenage boy living in England. His Mum (Felicity Jones) has been struck by cancer. Soon the treatments stop working, and she has to start spending most of her time at the hospital. Conor’s Grandma (Sigourney Weaver) shows up to help with her daughter’s care, and prepare for the day when Conor has to move in with her.

Conor himself is an artistic kid, probably the type to be wrecked by deep emotions under normal circumstances. On the hill outside Conor’s bedroom window is an old church and graveyard with a massive yew tree, and the boy has nightmares about standing on the hilltop when a giant sinkhole opens beneath him. Grandma, meanwhile, is a ferociously poised British lady who runs a well-put-together upper-class home, full of beloved antiques. She’s also up to something in that room at the top of the stairs. Needless to say, Conor and his Grandma do not see eye-to-eye.

One night Conor is sketching fantastical creatures on his desk, when suddenly the pencil falls to the ground and rolls to the window, as if it’s caught in some weird gravity well. Conor looks out, only to see the yew tree stand up, shake off its leaves, and rise to form a monstrous humanoid creature made entirely of snarled roots and branches. The Monster strides down to Conor’s house, punches out the boy’s wall, hauls him outside, and promptly strikes up a conversation (voiced by a bass-enhanced Liam Neeson). Apparently Conor’s distress has called the beast forth. So the Monster will tell Conor three tales, and the Conor will tell the Monster his truth.

It’s established pretty quickly that the Monster only exists in Conor’s head, and their encounters are imaginative dream sequences. Occasionally, the Monster seems to possess or become one with Conor, like when the boy finally beats the crap out of a much larger bully at school, or trashes Grandma’s den in a fit of emotional catharsis.

You can see where this is going: The Monster becomes an oddball therapist so Conor can get in touch with his own inner monster and make peace with his mother’s looming death. That episodic structure takes up most of the rest of the film.

The material is familiar but well-executed. McDougall is a wonderfully expressive young actor, and a convincing anchor for the story. Weaver buries Grandma’s emotions under an iron mask, and her utterly silent reaction to Conor’s destruction of her house is laden with portent. Director J.A. Bayona shoots her in a way that puts us in Conor’s headspace, dreading a blowup that never comes. When Ness’ script finally delivers Grandma’s turn, it lands with force.

Jones doesn’t get as much to do as Conor’s Mum, but she and the makeup crew make the ravages of cancer strikingly visceral. And after The Theory of Everything and Rogue One, I’ll welcome her presence in anything.

Toby Kebbell also shows up as Conor’s dad, long divorced from his Mum, and living in America. Both Conor’s parents are young, and it seems likely Conor’s father was a cad besotted by his own handsome cleverness, and wasn’t a good husband. Yet now the dad is a bit older, with decency and some self-awareness, and realizes his role in all this is to provide Conor both a friendly male outlet and a steady hand.

Bayona uses shadows, color, camera placement and crisp cinematography to give A Monster Calls a subtle and appropriately otherworldly feel. The Monster himself is not quite photorealistic, but he has artistry and a very clear personality. The most striking parts of the movie are the Monster’s tales, which are animated in an homage to Conor’s own sketch work and watercolors.

Ultimately, the film is yeoman’s work, bringing craft to a modest and heartfelt children’s story. It’s not going to knock anyone’s socks off, and it barely has a plot. But it knows what it wants to do, comes up with some nice visual metaphors, and sets its pieces up properly for the climax. The final reveals are not unexpected, but they have weight. There is grace in the suggestion that, just maybe, this wasn’t in Conor’s head after all.