It really is amazing just how epic this serial feels. We're five episodes in, and already we have traveled from the Himalayas to Cheng-Ting and taken in sandstorms, oases, treachery, hidden caverns, and sub-plots galore. We've had what feels like a massive cast and tons of incident, and Shang-Tu and Kublai Khan loom ahead with all the weight of 150 solid minutes of foreshadowing. This is the episode where all that momentum really starts to pull the story forward towards its conclusion.
Which isn't to say it's perfect--the bandit fight is a tense sequence, but the whole "let's scare the superstitious peasants by popping bamboo at them" strategy is a bit embarrassing in that way that treating everyone from The Past as superstitious peasants always is. Luckily, that's not the only thing going on here; Tegana shows he's not just a panto villain in a kiddie show by ruthlessly sacrificing his compatriots to preserve his ruse. He also shows himself as clever and adaptable--when his first ploy, canceling the raid to discredit Ian, fails due to Acomat's impatience, he's willing to change tactics and ingratiate himself further to Marco Polo.
The scene with Ian and Marco bears special mention as well, as it's a good example of the kind of characterization this story does well. The two men are clearly comrades, in an era of the series where Ian is treated credibly as a second protagonist (it's unfortunate that Barbara is mostly sidelined in this episode and to some extent in this entire story), and the speech between them shows a respect and admiration that clearly makes them wish their goals didn't conflict. Which leads also to the wonderful scene where Marco asks for their promise to cease trying to steal the TARDIS...and each of them respects him too much to lie to him. (And where he displays a common-sense, healthy distrust of Tegana by refusing his offer of bodyguarding duties. In one brief moment, we're made aware that Marco knows he has no true allies on either side.) The dynamics of this story really do make it a highlight of the "circumstances have separated us from the TARDIS for X episodes" era of the series.
And in an episode filled with so much plot and character development I almost can't fit it all in, I also want to bring special attention to Tegana's character once again. He's an interesting twist on the "superstitious peasant" trope that I disdained just a few paragraphs ago. Ian points out that he can't be after the TARDIS because he believes it to be magical and he's terrified of it, and he's both very right and very wrong. Tegana isn't faking his superstition about the TARDIS; he genuinely does believe it to be a magical artifact created by a wizard with evil magical powers. But it's exactly that quality that makes him want it so badly--Tegana believes that with the TARDIS' power, Noghai will gain a decisive advantage over Kublai Khan. His superstitious make him more dangerous, not less, because Lucarotti understands that superstition and stupidity don't necessarily go hand in hand.
And then there's Ping-Cho, who suddenly steps to the forefront and gains agency in a story where she has conspicuously been denied it at every turn. She still has no control over her own life, but circumstances put her into a position where she has both a moral dilemma and the power to bring hope back to her only friend. (Although it does put the idiot ball squarely into Marco's hands--why not just re-hide the keys?) Her inventive solution to the moral dilemma is obvious equivocation, but it's also an entirely understandable character beat that shows just how deep the characterization is for all the cast. This really is an ensemble series at this point, with the incidental characters just as important as the regulars.
Oh, and there's a great cliffhanger too, with Susan under threat for the entirely understandable decision to repay her friend's kindness with a small gratitude. Ping-Cho asked for only one thing in return for stealing from Marco and possibly earning herself a dreadful punishment, and Susan refuses to leave without giving it to her. It's a risky thing to do, but not a foolish one, and deeply rooted in everything we've seen about Susan so far in the series. Shame it's gone so badly for her.