The hook of Hijack has always been a claustrophobic setting, where the confinement of the space forces characters to confront their inner demons. In Season 1, it was a plane, while in Season 2, it's a train. Ironically, this season has started to improve by expanding its viewpoint. I appreciate the thought put into inverting the core premise to avoid feeling like a retread of the first outing, but I still maintain that what's happening on the train isn't that interesting. However, Episode 4, "Switch," helps with that by introducing a murder-mystery angle after Freddie's death and lending more focus to Mei, the only person on board who knows that Sam isn't the nutcase he's cosplaying as.

The bulk of "Switch" broadens its off-train horizons, taking in multiple characters and factions that are related but not directly involved. It gives Marsha a bit more screen time and her predicament a bit more clarity. This helps the bigger picture to cohere into something more legible, making the world feel livelier and more connected.
I also think this episode has the best version of Sam Nelson. Initially, his predicament meant that he was having to play too aloof to root for. But since the reveal that he's being pressured with threats to Marsha's life, he has a bit more to play. Now he's the good guy having to spin multiple plates, making himself a believable hijacker to the passengers and the control room, but also doing whatever he can to be compassionate and prevent any more sudden murders. It gives Idris Elba more nuance to work with, and that, in turn, makes the drama work better.
And the drama is becoming pleasingly complicated on the train itself. I still believe that the major problem there is that the show hasn't done a fantastic job of introducing compelling characters on it. So the ultimate reveal about Freddie's killer doesn't really land because it doesn't turn out to be anyone that we're familiar with. Outside of Mei, nobody has a real personality. We fret for the kids because they're kids, but I'm not especially interested or invested in anyone on the train.
What's compelling in Hijack Season 2, Episode 4 is how these various elements interlock and inform the core drama. Sam's familiarity with Mei gives him the opportunity to consider one of the passengers a potential ally, but he also has to weigh up whether putting her at risk is the right thing to do. There's a sick baby that tests how far Sam is willing to take his bad guy routine, but he also has to figure out how to spin the altruistic gesture of allowing the baby off the locomotive into an advantageous move for him. He's also trying to balance keeping the passengers intimidated enough to prevent any heroics and calm enough that they don't cause chaos, all while privately nursing the anxiety of there being a bomb under the train that might kill them all.
These concurrent threads converge into a riveting tapestry of pivotal revelations and dramatic developments as "Switch" nears its conclusion. The revelation that Freddie's murderer isn't the obvious long-haired suspect, whose bloody hand was merely the result of a cut incurred while attempting to conceal a bag of drugs, but rather the seemingly innocuous medic who offered to assist him and remained on the train unaware that Sam had uncovered her true identity, adds an unexpected twist. The train's necessity to switch tracks in order to stop at an abandoned station to reunite the baby with its mother presents Sam with an opportunity to bring John Bailey-Brown aboard under the pretext of offloading the infant.
Furthermore, the identity of Marsha's true tormentors is finally revealed, reviving the presence of Daniel O'Farrel and Zahra Gahfoor. The man whose car Marsha attacked in the previous episode is actually working for the former in an effort to protect Marsha, rather than being a threat himself. The real danger turns out to be her seemingly kind neighbors, who - we presume; it happens off-screen - use a shotgun to kill her would-be bodyguard at the end of the episode.
While I have been critical of Season 2 of "Hijack," I must admit that it's shaping up quite nicely now. With several episodes still remaining, there's ample time for the story to take further intriguing turns.