Both the two Asian period war dramas opening in cinemas here this week lose the battle to hang on to a coherent plot despite lavish set designs and top-notch casts.

In fact, they seem to be swept away by the epic grandeur of their settings.

South Korea's Assassination, in particular, has such an unwieldy and ambitious storyline involving everything from doppelgangers to double agents, it completely loses the viewer within the first hour.

It is only when the action of the titular assassination plot kicks in in the second half, that things get a bit more interesting, albeit unfolding like a standard thriller.

That did not stop the movie from becoming a huge success in its native country. It opened there two months ago, beating Hollywood blockbuster Avengers: Age Of Ultron to become the No. 1 film of the year.

As in his 2012 hit heist film The Thieves (2012), director Choi Dong Hoon sticks to the same formula of employing a huge ensemble cast here. This means introducing a lot of minor characters at once, most of whom are so thinly drawn that they are completely forgettable.

This was less of a problem in The Thieves because its jocular tone gave several of those characters entertaining one-liners to spout.

The mood in the new movie is a lot more sombre - most of the side characters do little more than show up and mouth some speech in archaic language before disappearing again.

It is a good thing that leading lady Jun, who had also headed The Thieves cast, does enough to hold the fort, so compulsively watchable is she as a no-nonsense army sniper here.

Much like how her performance had lifted the sappy but hugely popular 2013 TV melodrama My Love From The Star, her presence is the only bright spark about this work.

In the Hong Kong historical epic A Tale Of Three Cities, the sizzling chemistry between Tang Wei and Lau Ching Wan is equally crucial to the film's success.

Their ill-fated romance, which takes them from Anhui to Shanghai and then Hong Kong in 1930s war-torn China, is moving and believable, even if they appear utterly mismatched at first (she is too fresh-faced for his rugged vagabond persona).

Just when you think it is impossible that their story could be this melodramatic - too many too-neat coincidences and near-death close shaves - you discover that the film is loosely based on the star- crossed relationship of the parents of Hong Kong superstar Jackie Chan.

Chan's mother in real life was allegedly a hard-drinking gambler while Tang's character is a lot sweeter. It is only when the camera pans away from the couple that the film fails to work.

The subplots, from Lau's espionage adventures to the blossoming romance between the pair's friends (played by Jing Boran and Qin Hailu), serve only to distract viewers from an otherwise arresting love story.