A teenage fantasy novel about a post-apocalyptic underground city, jolted to screen life by the scribe of Burton’s finest fantasia Edward Scissorhands and the director of the punchy CG kid-flick Monster House? Starring the can-do-no-wrong Bill Murray as the conniving, greedy-guts mayor of the subterranean metropolis?

On the surface, it appears Ember has flicked all the right switches. But this is a family adventure powered by an energy-saving, 40-watt bulb. Still, it’s not without some enchanting gleam… Living underground for 200 years and keeping the flame of humanity alive has turned Ember into a chirpy, industrious hive of happy-clappy citizens who don’t question their lot. But the gargantuan generator keeping scruffy Emberites alive is way past its sell-by-date and has started to pitch their glitter-grunge universe into bouts of scary, flickering darkness.

Saoirse Ronan (Atonement) makes a plucky tomboy heroine, tearing through the cobbled streets on messenger duties and linking up with pipe-worker Harry Treadaway to unravel the mysteries of the dying city’s dwindling food stores and why Mackenzie Crook is wearing such crappy, dime-store teeth. It’s not just creaky facial props, though. There’s something unsatisfying about the higgledy-piggledy, set-constricted realisation of Ember, while the film itself is light on genuine thrills – there’s one boisterous chase by a random, CG mole-beast, a plunging log-flume escape... and that’s your lot, really.

As for the stack of name support players (Tim Robbins, Martin Landau, Toby Jones), they whizz by in a blurred haze of truncated screen time and dispensable purpose, while Murray gives a flat-footed portrayal that cries out for more of his zesty, deadpan comic anarchy. Like too much of Ember, he’s sorely underpowered.