Guard (Kim Woo-bin) and his robot sidekick Thunder (voiced by Kim Dae-myung) are on the ground tasked with monitoring these secret inmates, rounding up those able to escape their anthropomorphic prisons, but otherwise getting pretty despondent with their solitary station.

Guard is also equipped with a crystal-like device enabling him to travel back in time and monitor POWs in the Goryeo era of Korean history. On one such trip, Guard and Thunder retrieve a newborn baby who is orphaned by an escaped alien, and 10 years later, lives with them as Guard’s surrogate daughter (Choi Yoo-ri).

Back in the late 14th century, hapless Taoist wizard “The Marvellous Muruk” (Ryu Jun-yeol) hears about an all-powerful crystal known as the Divine Blade. He soon teams up with a mysterious pistol-wielding woman (Kim Tae-ri) known as “The girl who shoots thunder”. Numerous other interested parties appear, also looking to get their hands on the fabled weapon.

The effects work here is first-rate, as one would expect from one of Korea’s most expensive productions to date, but the script’s central conceit starts to buckle under the slightest scrutiny.

Choi’s stacked ensemble cast includes So Ji-sub, Yum Jung-ah and Kim Eui-sung, ensuring that Alienoid remains an entertaining romp throughout.

The discovery that, after 142 minutes, the story remains only half told reconfirms Choi’s intent to boldly go where no Korean film has gone before.