Despite a few modish touches, this feels fundamentally very old-school, and not necessarily in a good way, right down to the repeated shots of people running away from fireballs in the background.

One plot line veers towards fantastical science fiction, but it's presented entirely seriously. It's an overwrought concept, conspicuously patched up by flashbacks and expositional dialogue.

The film's corkscrew plot becomes a little weighed down by all the flashback narrative reveals, but the crazier the revelations, the more fun it becomes, before it powers full steam towards a thrilling finale.

Yau opens the movie with a glorious and hilariously pointless explosion of Hong Kong International Airport, mostly just to prove that he can put it to film.