Something has gone terribly wrong in the magical kingdom of Narnia. The new film adaptation of C.S. Lewis's classic 'The Lion, the Witch and the Wardrobe' was a moderately well-received charmer; 'Prince Caspian' showed diminishing returns; and 'Voyage of the Dawn Treader', judging by the reviews and last weekend's dismal box office returns, was not a movie anyone much wanted. What happened? Why did this eagerly awaited film franchise turn into such a bust, and how did American audiences so quickly lose interest?

I want to suggest that the 'Narnia' films, the third one in particular, fail as works of fantasy. They don't know what to do with magic, which is, after all, Narnia's defining characteristic. To see why this is, it's useful to compare 'Narnia' to 'Harry Potter', a more recent classic that has spawned a far better and more successful movie series.

In 'Harry Potter', magic is hard. It's both an art and a science. The characters spend years training to master it and bend it to their will; some never succeed. There are rules. Things go wrong: spells don't work as expected; potions have flaws and unpleasant side effects. In this universe, magic is more than a series of impossible things happening at the random behest of the plot. It means something; it has structure, and it gives the movies structure too.

Consider the raid on the Ministry of Magic that is the wonderful centerpiece of 'Harry Potter and the Deathly Hallows' Part 1'. In this lively sequence, Harry, Ron and Hermione use Polyjuice potion to disguise themselves as Ministry employees, sneak into the Ministry, and retrieve the horcrux locket that, it turns out, Dolores Umbridge wears around her neck.

The key here is that we already know – from earlier in 'Deathly Hallows', as well as from much earlier in 'Harry Potter and the Chamber of Secrets' – how this bit of magic works. We know that they will need a hair from each of the people into whom Harry, Ron and Hermione want to transfigure. We know that the potion will not disguise their voices, making their plan that much more challenging. We know that they'll have a limited amount of time before the potion wears off, leaving them exposed. From there, the scene practically writes itself. It's not just magic; it's magic we're invested in. It's engaging, suspenseful storytelling.

In Narnia, by contrast, there are no rules. In this "magical" place, anything can happen at any time. Prince Caspian actually says so at one point in 'Dawn Treader'. A good example is the section of the third film where Lucy, Edmond, Eustace, Caspian, and the rest of the Dawn Treader's crew land on the island of the Duffers – random and useless little creatures who appear out of nowhere, make a bunch of noise, and go away never to be seen by us again. The Duffers kidnap Lucy Pevensie and instruct her to enter an invisible mansion where she is presented with a Book of Incantations. We have never seen this book before, and neither has Lucy. Nonetheless, she opens it, and starts reading spells, which are written out in plain English ("a forgetting spell," " a spell that cureth toothache," etc.). Immediately stuff starts happening – first, snow starts falling; then Lucy is transformed into an image of her beautiful older sister. It's magic.

This is essentially the problem with the whole franchise. Magic exists here to show off fancy effects and teach easy lessons. There's nothing to it. The point of the scene is for Lucy to rise above her low self-esteem and abandon her unhealthy envy of her older sister – so the movie manufactures some magic to quickly make it so, and then just moves on to something else equally arbitrary. Later someone randomly turns into a dragon, a star falls from the heavens to tell the characters what to do, and Aslan finally shows up to deliver the requisite Christian undertones.

C.S. Lewis' novels weren't great in this regard either, but they were a little better – the Book of Incantations, at least, does show up elsewhere in the saga. The movies are shameless. The notion of "magic" is not carte blanche to do whatever you want. Fantasy should build coherent worlds and tell coherent stories. This is where 'Harry Potter' succeeds and 'Narnia' fails. It's all in the magic.

Harry Potter and the Deathly Hallows: Part I
Based on 42 critics

Harry, Ron and Hermione set out to destroy the Horcruxes, the secrets to Voldemort's power. Read More

The Chronicles of Narnia: The Voyage of the Dawn Treader
Based on 33 critics

A painting draws Lucy (Georgie Henley), Edmund (Skandar Keynes) and their cousin into Narnia again. Read More