Infinity Train rumbled onto Cartoon Network in August 2019 with an intriguing premise: a girl unwillingly sucked into an adventure on train where every car is a different universe with different rules, and every other prisoner has a glowing number on their hand. Like most of the wandering residents, she just wants to get home, and she spends the first season exploring the train and trying to understand why she’s there.
The first season set up the train, and with each subsequent season, creator Owen Dennis has built on that first story, exploring more of the mysteries that make the train work, and telling more complex stories about the characters who board it. After Infinity Train landed on HBO Max for a third season, there were rumors that the series had been canceled. But in March, Dennis revealed that season 4 was on the way — and that while he and the team had enough stories planned for eight seasons, this will be the last one made.
Even with all the lingering questions, this final season of Infinity Train (subtitled Duet) doesn’t divulge any new, shocking revelations about the train in the same way the show’s previous seasons did. In fact, more so than ever, the mechanics of the train take a back seat to the relationship between the protagonists. As with the previous installment, the two main characters have a pre-existing relationship that gets tested on the train. But while Book 3 was a tragedy, unraveling a toxic friendship, Book 4 focuses on rebuilding its central relationship after it fractures.
The result is the show’s most emotional season, and also its most heartwarming. Duet speaks to the ethos at the core of Infinity Train: that we all have a chance to do better and get better.
[Ed. note: This review contains minor setup spoilers for season 4 of Infinity Train.]
The passengers this time around are two best friends: free-spirited Ryan and responsible Min-Gi. In their childhood, both boys dreamed of becoming rock stars, but while Ryan sets off on a cross-country tour to try and make it big, Min-Gi works at a local chain restaurant and prepares for college. The action kicks off when Ryan books a gig in New York and returns home to persuade Min-Gi to come with him. After an argument, they wind up aboard the mysterious train in matching grey jumpsuits, sporting matching glowing numbers on their hands. According to train denizen Kez, a bubbly, floating, talking concierge bell, two passengers coming aboard at the same time with the same number is basically unheard of.
At this point, fans of the series know the drill: New passengers wake up on the train, figure out the life issues they need to fix, and get their numbers down to zero by confronting those problems, all while traversing the train’s wacky pocket-dimension cars, each with their own task at hand. But while Ryan, Min-Gi, and Kez embark on their share of fantastical adventures — feeding a giant, squealing baby pig voiced by J.K. Simmons, for one — the train doesn’t get interrogated nearly as much as in previous seasons. Instead, the core struggle is between the two friends.
This time around, it isn’t just the train mechanics that are obvious. In Duet, the passengers’ pasts aren’t treated as mysteries. Book 3 teased the main characters’ sad pasts (without ever fully delving into either) to explain why they unravel the way they do, revealing more about the characters as they spiral or grow. But Book 4 presents Ryan and Min-Gi’s relationship in the first episode, literally starting from the day they’re born. Both friends care for each other, but their conflict stems from their choices: Min-Gi sacrifices his dreams to please his parents, which Ryan takes personally. Ryan flies into situations headfirst without thinking, which Min-Gi sees as reckless and inconsiderate.
Book 4 is about healing. That doesn’t mean it’s all fun and games. Min-Gi and Ryan must confront ugly truths and have difficult conversations to repair their friendship. As usual, the train forces their problems to come to light, whether by helping Kez confront her own problems, or via a particularly chilling car that takes the form of an empty art gallery with shadows that whisper to the boys, augmenting their most sinister thoughts. The story gets dark — almost as dark as the tragic Book 3.
Questions about the train still linger. They might never get answered, since Book 4 is reportedly the end, this time for real. Characters and plot points from previous seasons that were left dangling don’t get tied up. But since Book 4 ends without new questions or dangling cliffhangers, it ends up as a fitting conclusion to the Infinity Train saga. If all the questions about the train were answered, it might lose its mystique and appeal. Instead of finishing the show by stripping away the train’s mysteries, Dennis and his team use the last season to showcase the train’s true purpose and end the show with that uplifting message.
Infinity Train: Book 4 — Duet will stream on HBO Max on April 15.