Imagine if one day the world went dark and the entire population was left helpless, except for the small hope of an underground city: Ember City. This is the premise of director Gil Kenan’s new film “City of Ember,” based on the young-adult novel of the same name by Jeanne DuPrau. A portion of Earth’s population moves to Ember, a glittering metropolis, “for the good of all mankind”—or so say The Builders, the team that masterminded the city. Although the film disappoints at times with flat supporting performances and under-developed background, “City of Ember” ultimately uplifts with its strong central relationship and hopeful tone.

Two hundred years later, hope is diminishing as the generator—the city’s power source—starts to fail and Ember begins to fall apart. As one citizen dismally notes, the “city is going black for good,” just like Earth. All hope is lost until an unlikely friendship is born between Lina, played by Saoirse Ronan, and Doon, played by Harry Treadaway. The pair discovers one of the city’s most ancient secrets and the key to their survival. Their adventure, fueled by Lina’s love for her baby sister and Doon’s desire to help the human race, takes place under, around, and through the city, unveiling the secret escape from the City of Ember.

Ronan, who previously earned an Oscar nomination for her supporting role in “Atonement,” has proven her merit once again. Her performance is heart-warming and inspired, and she becomes the shining star of the movie. Unfortunately, the rest of the cast, which includes Bill Murray, Tim Robbins, and Marianne Jean-Baptiste in secondary roles, is disappointing. Murray, whose melancholy performances are always balanced with humor, is unfunny and unconvincing in his role as mayor of Ember City.

Also frustrating is the film’s lack of a believable backstory; integral information is incessantly missing from the plot. What happened to the world last time? What made it fail? So many questions go unanswered that it can at times be somewhat tiresome.

Even so, the movie does address certain concerns that mirror issues of the world today—one such concern being what the government is really doing and what information they are withholding.

Another strength of the movie is composer Andrew Lockington’s original score. His fast-paced and jumpy music carries the movie, making the viewer anxious about what will happen next. Although our anticipation is not always satisfied, Lockington contributes as much as he can to the overall impact of “City of Ember.”

Doon’s father, played by Robbins, advises him, “If you have truth, you have to pursue it.” It is this idea that is perhaps the movie’s most inspiring. To be willing to risk everything in the pursuit of truth and protection of mankind is audacious, but also noble. Lina’s big heart and Doon’s obsession with the beauty and complexity of the generator and The Builders create the perfect dynamic to unveil this world-altering secret.

And yet, it’s almost hard to believe that people would want to leave the fascinating place that is Ember City. Its inhabitants are not aware of Earth’s glorious miracles like sunsets, fall foliage, sunny days, and starry nights; what could possibly be appealing about the unknown and dangerous darkness outside when one’s home “is the only light in a dark world,” as the mayor puts it?

As the adventure winds down, the movie ends with a fantastic scene that leaves the characters and the audience with a sense of awe, but also—and more importantly—hope for a brighter future. Finally, the film’s heroic pair finds “the beacon of light in a world of darkness.”