The Captain (Hoa) struggles with conflicting identities throughout The Sympathizer. He is biracial, born to an impoverished Vietnamese mother and absent French father, which sets him apart from his countrymen and provides a constant source of torment and ridicule.

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He is also a spy, embedded by the Viet Cong in the South Vietnamese army. In the days leading up to the fall of Saigon, he is serving as aide-de-camp to “The General” (Toan Le), chief of the secret police.

While nominally rooting out Northern agents operating in the city, he secretly sabotages these investigations to protect his comrades while relaying any usable data back to his superiors in Hanoi.

The end of the war offers no respite for the Captain. After securing safe passage to America for the General and his family, his efforts to evacuate his two best friends ends in disaster.

Man (Duy Nguyễn) vows to remain in the country and continue fighting for the communists, while Bon (Fred Nguyen Khan), a paratrooper for the South, loses his wife and newborn son to artillery fire as they attempt to board the plane.

Once in America, the Captain is ordered to continue his surveillance of the General, and file regular reports with Man using invisible ink. But many of the refugees, the Captain and General included, are soon seduced by the intoxicating capitalism of the West.

All this is relayed in flashback, both to the audience and, as it transpires, to the Captain’s interrogators.

At some point after his evacuation, the Captain returned to Vietnam and fell foul of his own communist handlers. Now captive in a reeducation camp, not as a prisoner but an “educatee”, he is forced to transcribe every detail of his experiences.

But time, it seems, has poisoned his perspective, and the Captain can’t help but write an even-handed account, expressing compassion and understanding for both sides of the campaign – much to his captors’ chagrin.

Therein lies the key to The Sympathizer’s success. The Captain is a wholly unreliable and untrustworthy narrator who repeatedly forgets, misremembers, and deliberately manipulates the facts to protect himself and those around him.

Simultaneously, he is being similarly used and exploited by those in his orbit, including the General, his daughter Lana (Vy Le), an opportunistic Major (Phanxine), a left-leaning journalist (Alan Trong), and the many duplicitous antagonists played by Downey.

Over the course of the show, Downey embodies CIA agent Claude, an effete college professor pushing an outdated perspective on “Oriental Studies”, a gung-ho congressman known as “Napalm Ned” and, perhaps most entertainingly of all, a self-aggrandising film director who hires the Captain to be his Vietnamese consultant on an Apocalypse Now-esque war movie.

One of the most bravura sequences of the entire show transpires at the climax of episode 3, when the Captain’s on-set role is negotiated in the back room of a debauched Los Angeles club by all four Downeys at once.

The Sympathizer wields incredible dramatic heft between moments of uproarious levity and dazzling, cinematic flair. Hong Kong audiences reared on thrillers that champion undercover agents and noble anti-heroes will delight in its densely layered narrative of confused identity and divided loyalties.

More than half of the spoken dialogue is Vietnamese, and the production has gone out of its way to cast local talent wherever possible.

The novelty of this approach is addressed repeatedly during the movie shoot sequences, not least when an extra playing a Vietnamese villager blurts out her lines in Cantonese, which goes completely unnoticed by the oblivious crew until the Captain is forced to step in.

Admittedly, there are moments in the later episodes where the dramatic urgency of the narrative starts to ebb ever so slightly, but for the most part The Sympathizer is a bold and hugely rewarding tale.

Park and fellow directors Fernando Meirelles and Marc Munden have crafted a richly detailed period piece that offers insightful commentary on the immigrant experience within a thrilling tale of espionage and spy-craft.

Anchored by a complex, star-making turn from Hoa Xuande as the eponymous spy, The Sympathizer is, as the Captain’s mother repeatedly reminds him, half of nothing, but double of everything.

The Sympathizer will start streaming on HBO Go on April 15.