Underestimating Helena has always been a terrible idea, and in this episode the Proletheans learn why. Not only that, but Rachel makes a huge move that is certain to drive Sarah to new extremes in her war against the Dyad Institute.

First up, though, is the ongoing rediscovery of why Alison and Donnie work so well as a couple. This week, they’re burying Dr Leekie together. It’s a fun and fairly inconsequential diversion as the pair figure out what exactly they’re going to do with the evidence, concluding that they should bury him in their own garage. It’s both a terrible and rather smart plan, as nobody’s likely to find him there but it’s about as incriminating a location as possible to hide a body.

Season 2’s least interesting subplot has been Angie’s attempts to work out what is going on with the clones, and she’s still on the sidelines here. There’s a way her story could have been an interesting look at what it’s like to be on the outside of this craziness but it hasn’t worked out that way.

Her insistence on using Vic as a mole has tied her to Orphan Black’s least welcome character, making much of this material dull. Fortunately, Donnie (fast becoming one of the show’s best characters) is there to tell the detective to end her unlawful investigation and scare the living daylights out of Vic. His assertiveness reignites Alison’s love for him, suggesting that his murder of Leekie might, oddly, be the thing that mends their relationship.

Finally, we get to find out what Helena’s been up to and the developments this week do not disappoint. This group of Proletheans and Henrik are revealed to be just as fanatical and dangerous as the last lot, with Helena’s vicious and fiery reaction ultimately feeling completely justified. Henrik is a slimy creep, and he gets a taste of his own invasive experimentation before Helena burns down the firehouse with him inside. Presumably, his family are also left inside (aside from Grace and Mark), but that’s not something we are explicitly told in any way.

The one thing that remains true is that Helena is not one to be underestimated. She’s far too unpredictable to be the subject of an experiment, and Henrik is wrong to think he can control her. He gets a lesson in just how much control he really has over her when she exacts her vengeance on him. One of Orphan Black’s central messages is about how individuals should have the final say when it comes to their bodies. Henrik takes that away from women, but Helena’s not letting him get away with it.

While Kira is ultimately given the choice over whether she’ll give her bone marrow to save Cosima’s life, it’s very much a situation created by Rachel that turns Delphine into an  uninformed pawn and takes advantage of Sarah’s hope that she can save her sister from the fate the disease has in store for her.

The ensuing events are reminiscent of how last season’s excellent finale ended, on the notion that Kira had been kidnapped by Rachel. It’s not until this episode, though, that it really happens. Kira has always been at the centre of Dyad’s plans, and seeing her taken after a season full of people trying to keep her safe just makes the impact of the development even more affecting. We have more knowledge now of who Rachel is, and it’s unsurprising to see that her decision to steal Kira seems to be something of a response to her feelings about not having a mother and not being able to be a mother.

There’s really no telling what will happen next. Helena’s headed back to Sarah and it’s easy to see the two of them going up against Rachel in a situation where Sarah is less likely to caution Helena about pulling the trigger. Cosima’s life remains on the line, and Duncan is making it clear that he won’t have his research pored over by the Dyad Institute.

Orphan Black continues to excel by challenging our expectations, and it’s certain to have a few more surprises up its sleeve for next week’s finale.

Aired at 10pm on Wednesday 25 June 2014 on BBC Three.