During the 1950s and ’60s, the spectre of nuclear war loomed large. Nations were crippled with fear and paranoia, constructing nuclear fallout shelters to sustain the population for months, if not years after an attack. Jeanne DuPrau expanded the idea of subterranean refuges in her first novel, The City of Ember, which was eventually published in 2003. In this first book of an ongoing series, she imagined an entire underground community powered by a massive generator, cocooned from the apocalyptic horrors which befall mankind on the surface. The human race endures while the planet heals, and in time, survivors hopefully find their way back to the surface.

Director Gil Kenan (Monster House) accepts the unenviable task of bringing DuPrau’s vision to life, working closely with production designer Martin Laing and cinematographer Xavier Perez Grobet to realise an entire city of ramshackle homes and business, laid out in concentric circles, with a town square at the centre.

These gargantuan, three-storey high sets, created in a hangar on Belfast docks, are spectacular — shabby, rundown and bathed in light from hundreds of bulbs which mimic the sun, Ember convinces as a self-sufficient community on the brink of collapse.

For the past 200 years, the bustling metropolis has survived under the power of a generator, but food stores are dwindling and machinery is about to fail, threatening to plunge the sanctuary into eternal darkness. Graduate student Doon Harrow (Harry Treadaway), who toils in the pipeworks under narcoleptic mentor Sul (Martin Landau), tells his inventor father (Tim Robbins): “I will not sit around while Ember collapses. I’m getting into that generator, whatever it takes.”

Feisty classmate Lina Mayfleet (Saoirse Ronan), who lives with her Granny (Liz Smith) and young sister Poppy (Amy and Catherine Quinn), feels just the same, praying that Mayor Cole (Bill Murray) and his advisors will find a solution to the nightmare.

Instead, Lina stumbles upon the answer when she discovers a metal box in Granny’s cupboard containing badly torn, cryptic instructions. With the help of greenhouse keeper Clary (Marianne Jean-Baptiste), Lina and Doon attempt to decipher the clues and outwit the Mayor’s lackeys, Barton (Toby Jones) and Looper (Mackenzie Crook).

City of Ember feels a tad sluggish even at 94 minutes, with just two action set pieces (a close encounter with a giant tentacle-nosed rat at the midway point and a high-speed, log flume finale) to quicken the pulse. Digital effects are used sparingly, but are noticeable by their clumsiness against such impressive production design.

Ronan and Treadaway (both pictured) are endearing but we don’t spend enough time with either of their adventurous urchins to feel we know them before the grand adventure begins (not in earnest).