The plot is as predictable as it gets. It's one of those movies that Russians speak English to each other and the acting is mostly atrocious, but it's not trying to win any awards either. Scott Adkins is the best actor in the movie, so know what you're getting into. If you plan to watch it for anything but the fights, which are good but not as memorable as previous ones in the franchise, you will be disappointed.
Review of Undisputed 4: Boyka
