Terrorism, nuclear weapons, a stellar pan-Asian cast and a hefty $26 million budget ― “Helios” has all the right ingredients for a pulsating Hong Kong action thriller, but ends up amounting to much less than the sum of its parts.

The film is undoubtedly an ambitious endeavor, touching upon big issues like the inefficacy of international diplomacy and Hong Kong’s precarious position vis-a-vis mainland China. It attempts to bring together the action blockbuster and the noir by interweaving high-speed car chases and ear-splitting explosions with cryptic, semi-philosophical conversations on loyalty and power.

But “Helios” ultimately fails to orchestrate its populous cast, whose diverging storylines seem to spiral off in their own directions rather than come together in a coherent plot.

Featured at the fifth Beijing International Film Festival, the film is the second and much-awaited installment by directors Longman Leung and Sunny Luk, whose police thriller “Cold War” was the highest-grossing film of 2012 in Hong Kong.

“Helios” features an intergovernmental mission to recover the DC8, the world’s smallest nuclear weapon and a South Korean invention, which has been stolen by global criminal Helios (Chang Chen) and his lethal female partner Messenger (Janice Man).

Upon receiving news that the DC8 will change hands in Hong Kong, two Korean agents, weapons expert Choi Min-ho (Ji Jin-hee) and National Intelligence Service agent Park Woo-cheol (Choi Si-won), are dispatched to the city. A shaky alliance is formed with Hong Kong detective Eric Lee (Nick Cheung) and consulting physicist Siu Chi-yan (Jacky Cheung), with the common goal of safely returning the DC8. Then enters Chinese official Song An (Wang Xueqi), who has his own agenda of reestablishing the Sino-American power balance through the scheme.

What ensues is a lengthy display of diplomacy at its worst and thinly sketched patriotism as each country’s representatives flex their egos over drawn-out boardroom discussions. The encroaching threat of terrorism, rather than instilling a spine-chilling sense of doomsday, drags the movie on at a lethargic pace.

Despite solid performances by the actors, their characters are not sufficiently developed for them to have any real material to work with. Scenes that attempt to show the humane side of the criminal Helios and the inner turmoil of detective Lee are unconvincing at best, and only pile on to the ever-sprawling narrative ― which resolves itself in an all-too-predictable plot twist and a dampening cliffhanger.

While the story begins and ends with the two Korean agents ― played by actor Ji Jin-hee, best known for his role in the period drama “Jewel in the Palace,” and Choi Si-won of K-pop group Super Junior ― they are, for the larger part, accessories to the plot, popping up now and then for a few scenes of feeble bromance.

The film’s redeeming qualities, meanwhile, are its well-choreographed action sequences, courtesy of action director Chin Kar-lok, and tasteful cinematography by Jason Kwan. A 10-minute motorcycle chase through the night streets of Hong Kong; ferocious fight scenes with the femme-fatale Messenger, vigorously portrayed by Man; and picturesque shots of the city’s vivid urban scenery are all wrapped in an ambience that seems to radiate heat.

These assets, however, become jumbled up in a rambling narrative that struggles, and ultimately fails, to bring the story together.

By Rumy Doo (bigbird@heraldcorp.com)