Every now and again a film will kind of sneak up on you and take you completely by surprise. I knew my wife had wanted to see “City of Ember” at the cinema, but I had taken one look at the trailer and dismissed it out of hand. However, when it made a recent appearance on the Sky Movies schedule, I relented, thinking that, without the added investment of having to buy cinema tickets, a bucket of popcorn and perhaps more importantly, using up a rare night out, I could always fall asleep on the couch if I wanted to.

The film starts out with a flashback to a time when the fate of mankind is in the balance. An unidentified catastrophe is soon to make the earth uninhabitable, so a group of scientists (American obviously – they’re always American) create an underground city, called Ember, to which a select group of lucky souls will be sent – a modern day ark – to safeguard the future of the human race. A silver box, the contents of which are not known at this stage, is entrusted to the first mayor, with instructions to pass down the box from mayor to mayor until the timer – originally set at 200 years - reaches zero and the box automatically opens. However, with 47 years left on the clock, the mayor of the time – a Mr Podd Morthwart – suddenly expires and the line of succession is broken, as the box lies forgotten at the back of a wardrobe.

Neither initially gets the job they want (but they do manage to job such delightful careers as “potato peeler” and “mold scraper”), but they trade jobs – with Doon taking up a position at the Pipeworks, and Lina getting her coveted messenger job. Lina lives with her younger sister Poppy and her senile grandmother, while Doon lives with his somewhat jaded and downtrodden father, Loris. After the scene setting, the film really gets going when the silver box is found and its contents discovered. The children realise that the builders of the City meant for its citizens to return to the surface and that somewhere in Ember, there is an exit. What follows is a fantastical and well-conceived voyage of discovery (n more ways than one).

Lina Mayfleet is played exceptionally well by the young and talented, Saoirse Ronan, probably most recognisable for her role as the naïve but vindictive young Briony – sister to Kiera Knightley’s Cecilia - in Joe Wright’s period drama Atonement. There is a freshness and innocence about her performance that is paradoxically tinged with an air of maturity and wisdom. She is a believable lead alongside compatriot Doon and the film manages to avoid the over-emotional, saccharine sweet and mawkish acting that often afflicts these kinds of films. Doon Harrow, played by Harry Treadaway, was previously unknown to me, but he pulled off the role quite well and was convincing as the eager visionary frustrated by the inertia and blind faith around him. Doon wants to make things happen, but he is not the solitary driving force behind the adventure – Lina and he take it in turns to assume the led at various parts of the film and their interrelationship works well and remains plausible throughout (making allowances for the subject matter of course).

Despite this, it works well as a family adventure and will be enjoyed by school-age children and early teens as well as by their parents. There is little in the film that is truly scary or offensive (a close (but ultimately) comical encounter with a giant mole notwithstanding). So it warrants its PG rating. The acting is not going to win any Oscars, but it is a good, well-conceived and imagined story that is well told and it comes across as good, solid fare. The CGI is a little wanting in places, but this film is about the central story – so it does not distract from the quality or delivery of the film. The central theme is uncomplicated and easy to grasp, the characters are sympathetic and engaging, and the pay-off at the end is satisfying, if a little rushed and understated.

Despite my initial reservations, I actually enjoyed the film. Kudos to director Gil Kenan for whom this was his debut live action film (he directed the animated Monster House previously) who keeps the plot moving and weaves an enjoyable adventure in the modest 90 minute running time. That said, as a slight criticism, the main characters come across as a little underdeveloped and you are, at times, left wanting to know more about them. However, given its target audience and its modest origins, its an excusable oversight. If you’re looking for a fantastical family adventure with sumptuous sets and a cracking story to add some substance to the style, you won’t be disappointed by City of Ember.