After what looked like an uncertain future, one of K-pop's most beloved acts is back. Forward-thinking girl group f(x) returns with a new lineup and a fresh new sound via their comeback single "Four Walls."

f(x) typically delivers some of the best K-pop songs each year (2013's "Rum Pum Pum Pum" is a major standout in their discography) and this latest is no exception. Staying right on trend, the group employs a tropical-house feel while bringing their signature spine-tingling harmonies for the addicting chorus. Listen up for a few whistle tones towards the end.

The single premiered alongside its official music video, which showcases the four members moving through a mysterious, fantasy-like house and forest where the women move through the same exact storyline, but aren't together. It's only at the very end, when leader Victoria saves rapper Amber from dropping a teacup that she broke earlier, that we see the girls together, proving that they're better at each others' sides.

"Four Walls" is the first release of f(x) as a quartet. After six years as a fivesome, the group saw original member Sulli depart the group earlier this year after the singer dropped out of promotions during f(x)'s (also brilliant) "Red Light."

We're happy to report that the group's signature sauce is still intact and the refreshed lineup very well may have created their most addictive single in years. Here's to another six years, ladies.