The middle of Train to Busan is excellent. The first act is iffy, the ending is forced, but the middle is where the film excels. It’s where director Yeon just gets to do action, not getting slowed down with the humanity of it all (which he’s uneven on), and just executes these breathtaking action suspense sequences. Not just Yeon, editor Yang Jin-mo, photographer Lee Hyung-deok, composer Jang Young-gyu—and of course the actors. During the action suspense stuff, everyone does really well. Even lead Gong Yoo is good during these sequences and doesn’t have the overwhelmed look he gets the rest of the movie. Gong’s the only character with a real character arc—he goes from being a selfish hedge fund manager and bad dad to a hero in the fight against a zombie horde; he even becomes a better dad and reals everything he’s been missing in daughter Kim Su-an’s life. It’s ought to be emotionally devastating.

But Gong can’t do it. Being fair, it’s not like he gets any help from Yeon on it either, who doesn’t do a good job with directing the character stuff. Outside the action sequences, Yeon’s best directing is all on Ma Dong-seok and Jung Yu-mi, who play an expecting married couple caught up in the afore implied zombie apocalypse. Worse, Yeon’s adequate directing on Kim—as she experiences having this bad dad—falls apart as the film progresses. It’s like Yeon can’t pretend Busan’s about Gong and Kim patching things up thanks to a crisis situation and just sleepwalks the film through the series where they act like it’s working. Maybe it’s just a bad combination; the way Yeon directs the actors, the script, Gong’s flimsy performance. Because a lot of things do come together just right in other ways during Busan. Ma and Jung are wonderful. They’re both excellent—he’s a loving tough guy and she’s, well, okay, she’s just the loving tough guy’s pregnant wife, but she’s really good. And Ma’s able to carry the film when Gong can’t and the film acknowledges it, Gong acknowledges it. Yeon just doesn’t use it to further anything along. Top-billed Gong goes into the third act a better person but a thinner character; everyone else has more depth than him, with the possible exception of daughter Kim, just because she’s a plot device to keep him moving through the picture. Not in a craven way, just a very pragmatic one. Gong and Kim might be the A plot in the film, but all the other plots are more interesting, which becomes real obvious in the third act.

First there’s teen paramours Sohee and Choi Woo-sik, who barely get introduced during the film’s rapid-free introduction of the disaster movie cast—I mean, it’s zombies on a bullet train—have a little do at the beginning of the second act, but then get this layered C plot leading up to a heart-wrenching, loving conclusion. Very nice work from Choi and Sohee and from Yeon. He takes their C plot seriously. He also takes the out of nowhere and completely awesome conductor turns action hero subplot seriously. Jeong Seok-yong is fantastic in that part. Total surprise, but great pay-offs.

The supporting characters’ arcs always pay off (save businessman worm villain Kim Eui-sung’s arc, which goes on too long and gets too important) and always a with a little more enthusiasm than Gong and Kim get. Their family drama is basically red herring and not particularly tasty red herring because Gong’s so wanting at the dad stuff.

When Yeon makes it work—like with Gong, Ma, and Choi unintentionally becoming three musketeers and having to save people and get past zombies on the train and figure out how not to get bit doing it… great stuff. Great chemistry between the actors. It’s not just smooth, it’s easy. It feels like Yeon’s found the film’s vibe and he couldn’t possibility screw it up. He burns through all that newfound goodwill slow then fast; when he hits the third act, it’s a bunch of wide swings. They’d be fine, if they could just hit anything.

Train to Busan probably ends on its lowest point. It’s not bad, it’s got some strong performances, some great special effects—the “choreography” on the running, scary but silly zombies, is breathtaking—but Busan’s got problems pulling into the proverbial station. The third act’s just way too pat.