Planet of the Apes has proved to be an enduring screen franchise, from Pierre Boulle's novel to the film series of the 1960s and '70s, two TV series, a movie remake and a high-quality reboot. And now this sequel, continuing the newly told story. Perhaps it's the opportunities for both adventure and allegory that help keep it alive: behind the special effects there is substance, as in many of the best science fiction movies.

In a prologue, we're told the simian virus unleashed in the previous movie through medical experimentation has, over several years, devastated the human population of Earth. The newly intelligent apes and the surviving humans seem to co-exist in an uneasy peace.

In what used to be San Francisco, a colony of human survivors - apparently immune to the virus - are coming to the end of their energy resources. Malcolm (Jason Clarke) suggests asking the apes if they can reactivate the dam on their patch to create a new source of power but some humans, including former military man Dreyfus (Gary Oldman) are opposed and want to use their weapons to attack the apes.

But Malcolm successfully argues for the right to try things his way and enters negotiations with ape leader Caesar (Andy Serkis, in a remarkable CGI/motion capture performance). We soon discover the apes have the same divisions as the humans, with the cautiously co-operative Caesar being challenged by ambitious, man-hating Koba (Toby Kebbell).

It's a powderkeg of a situation and inevitably, a fuse is lit.

The film - directed by Matt Reeves (Cloverfield) - is a little slow at times and it's unnecessarily long. And the human characters - Rick Jaffa, Amanda Silver, Mark Bomback despite fine actors like Keri Russell and Kodi Smit-McPhee - are rather thinly drawn in the script.

But the parallels between apes and humans are fascinating, the emotional and power conflicts between and within the two races give the film its dramatic weight. There are lighter moments, too, but overall this is a serious film, using its amazing special effects to serve its story rather than simply to dazzle and bludgeon the viewer.

It will be interesting to see where the series goes from here: unlike some films, where sequels seem purely made for the money, there's real room for development.