One of the great things about Orphan Black is that we really have no idea just how many clones there are.

The only limit, really, is how many clones Tatiana Maslany can convincingly play. And, judging from what we’ve already seen, she can convincingly play just about anybody.

In this episode, we’re introduced to a surprising new clone, Tony. Tony is unlike the others, though, and he is the first transgender clone to be featured on the show. Introducing a trans clone is both something of a shocking development and one with a lot of narrative promise.

His story intersects with Beth’s, as the episode opens with Tony’s friend dying in a garage before telling him to find Beth. Soon after, he turns up at Felix’s place and both Art and Felix are trying to work out just how much Tony knows about the cloning conspiracy. It’s an interesting turn to take, but it looks like this may be our way into the military’s involvement in this whole thing (something that might finally give Paul something to do).

Expectedly, Maslany is superb when it comes to pulling off Tony’s distinctive mannerisms and abrasive personality. He even shares a scene with Sarah that continues to prove that Orphan Black’s star is one of the most multi-talented actors currently working in television. It’s difficult to envisage how she could be challenged any more than this.

On most other fronts, this is a slower episode than the previous few. We don’t even really get to see the fallout from Leekie’s death, as deceit has clouded the air so much that Rachel is yet to hear about what has happened and nobody but Alison knows how he really died. Cosima’s condition is only getting worse, though – the end of this episode makes the situation look dire – and Ethan is the only way a cure will be found.

While he’s now working with Rachel and the Dyad Institute to find a way to heal the clones, it’s made very clear that Kira’s bone marrow will make for a more effective temporary treatment (one that may be needed sooner than expected).

This is another episode without Helena, which is a shame. There are only so many clones you can fit into any individual instalment of Orphan Black though. It’s worth remembering that last year the show was primarily Sarah’s story and now it’s focused on telling substantial stories for all of the clones.

Alison getting out of rehab and back to real life proves to be an interesting plot thread, as she and Donnie begin to gradually tell the truth to one another and show that there might be hope for fixing their relationship after all. His revelation of Leekie’s body and Alison’s immediate reaction that it’s “not at all well-wrapped” is priceless (and it’s worth remembering that Donnie used Alison’s gun in the shooting, that’s definitely not good for her).

The lighting is incredibly dark in this almost every scene throughout this episode and there are no scenes set outdoors. Everything is closed in, whether that’s manifested through people being kept safe (like Kira, and to some extent Tony), people entrapping others (as Rachel does to Ethan) or people just trapped (like Cosima is, in that lab that seems to get smaller and more claustrophobic every time we see it).

As things go forward, it’ll be interesting to find out what motivates Ethan and how far he’ll go to save the clones from the disease. It still remains to be seen how the Dyad will react to the death of Leekie (expect Michelle Forbes’ Marion to reappear) and what the military’s role in this conspiracy is.

Expectedly, Orphan Black just piles on more and more intrigue and surprises in another top-notch episode.

Aired at 10pm on Wednesday 18 June 2014 on BBC Three.