Star Trek: Discovery takes an odd turn this week, delivering an episode that’s very much the Arsenal* of television science fiction: when it works, there’s little more pleasurable out there at the moment, but when it doesn’t, you’re bashing your head against a cascade of terrible decision after terrible decision.

The setup of the episode is a strong one: Burnham’s foster father (and Vulcan) Sarek is on a secret diplomatic mission to try and get a peace deal with the Klingons, but things go awry and he is lost in a nebula that looks like a jazzed-up version of those old visualisations in Windows Media Player.

This crisis allows us a look under the hood of both Burnham and Jason Isaacs’s Captain Lorca. Burnham’s Vulcan upbringing means she’s hooked up to Sarek’s katra – a kind of Vulcan soul – via some kind of existential wi-fi, so Lorca sends her into the nebula to see if she can find Sarek’s ship.

This she does via a poorly-explained Inception-ing (Vulcanceptioning?) into Sarek’s mind, where she sees replayed again and again the moment she was rejected by Vulcan’s equivalent of Starfleet. This event created a rift between Sarek and Burnham, as she had always blamed him – but repeated visits to Sarek’s mind eventually reveal that Sarek had done all he could, and it was barely-disguised racism that stopped Burnham from joining up.

This is all very interesting, but it all feels slightly contrived – being able to beam into someone’s memories because of a connection between your souls is only a few rungs away from saying that a wizard did it. We get some cool effects, and it’s 2017 so Burnham and Sarek have at it with some endearingly clumsy martial arts, but honestly, this would feel a stretch in Tolkien, let alone the theoretically more grounded Trek.

Also, the depiction of the Vulcans is odd: it’s fun to have references to Spock (bet the farm on a surprise Zachary Quinto cameo) and Mia Kirshner as Spock’s mum (the fifth actress to play this character – a record?) but at times this episode felt almost a parody. Sarek’s ship is blown up by – wait for it – “logic extremists.”

Now, the Vulcan’s have always been the most STEMlord of all alien races, but the repeated references to “logic ideology” and a Vulcan suicide bomber seem a reach to add a little too much contemporary resonances into the mix. Sorry, but a terrorist movement motivated by logic wouldn’t make it past its first meeting without arguing itself out of existence.

Still, the character beats work, even if some of the ideas are ridiculous. Far stronger is Lorca’s strand: welcoming Shazad Latif’s Tyler – his fellow POW last week – to the crew as his new head of security, he’s a man who both doesn’t care about conventional recruitment practices, and is concealing a serious case of PTSD.

This reveals itself over the course of his meeting with his superior Admiral Cornwell, which, like all chats with your boss, moves from work to in-depth psychological analysis to whiskey and, finally, casual sex. Lorca puts on a brave face, but when Cornwell touches his scars in bed, he panics and sticks a phaser in her face: not ideal behaviour for a man in charge of a key strategic asset.

Cornwell doesn’t mess about, saying she’s removing Lorca from command just as soon as she returns from the diplomatic mission she’s taken over from the wounded Sarek. This goes south, the Klingons take her prisoner – and Lorca, making the darkest decision of the show so far, rejects his crew’s suggestion of a rescue mission so he can stay in charge.

This is good stuff, with a pleasing moral crunchiness – although we seldom get to see the broken Lorca in private. Jason Isaacs is a terrifically self-possessed performer – check him out in The Death of Stalin as Zhukov – and this means that the public Lorca is so together that the private scenes of him freaking out don’t really land. If you see only one scene of his trauma manifesting amid literally dozens of him being the toughest captain in the galaxy, the scenes looking at his pain feel inauthentic. Still, one fault of almost all science fiction is that it ignores how war brutalises the survivors as much as it destroys its victims, and if a Quinto cameo is all but certain, you can be even more guaranteed of a redemptive arc for Lorca towards the end of the season.

Missing in action this week: the repercussions of Stamets’s ingestion of the genetic material of a space tick, and how his body’s use as a galactic sat-nav decoupled his reflection from his body. Or at least, any repercussion beyond his sudden cheeriness and willingness to drop words like ‘groovy.’ What’s coming first, Lorca paying the price for abandoning his superior officer/lover to her fate, or Stamets’s evil twin causing havoc?