Put simply: a romantic sci-fi parallel universe drama. The King of the "Kingdom of Korea" uses a magical bamboo stick to transport himself to the Republic of Korea, our Korea and quickly falls in love with a police officer there. There's somewhat more to it than that, but most characters have alternative versions and the difference between them all is very well done for the most part - with certain characters ("Unbreakable Sword") genuinely coming across as entirely different people.