Marianne (Marina Sirtis) is an actress, best known for her role in cult 70s sci-fi TV show The Dark Sublime. She’s done plenty of other acting work in the intervening four decades but the role of Ragana is the one she can’t shake off, even though to her, it’s the one that means the least. When Dark Sublime superfan Oli (Kwaku Mills) – who wasn’t even born when the series first aired on TV – tracks her down, an unlikely friendship develops. But what begins as an opportunity for Marianne to bask in the glory of her past ultimately forces her to confront the complications of her present, and in particular the unrequited love she feels for her best friend Kate (Jacqueline King).

One of the production’s biggest draws (the other being Mark Gatiss as the voice of a robot) is star Marina Sirtis, who is herself well known for playing the role of Deanna Troi in seven series of Star Trek: The Next Generation. While writer Michael Dennis didn’t create the role of Marianne specifically for Sirtis, he could very well have done, and this gives the character a sense of genuine depth; each time she expresses bewilderment at the unquestioning adoration of her fans, the audience understands that the emotion comes from a real place.

Real world parallels aside, Sirtis generally impresses with her portrayal of Marianne. Though she’s always quick with a witty comeback, it’s clear quite early on that the character is also really struggling to figure out where she fits in a world that no longer seems to have a place for her. Kate has a new partner – the younger, attractive, intelligent Suzanne (Sophie Ward) – and Marianne’s acting career seems to have stalled to the point where earning even £40 feels like a windfall. It’s little wonder she jumps at the chance to meet Oli, who idolises her Dark Sublime character and reminds her of who she used to be.

Speaking of Oli, Kwaku Mills is a delight, his charm and enthusiasm lighting up the room every time he’s on stage. Oli has issues of his own that mirror Marianne’s – he’s also in love with his best friend, but unlike Marianne, he’s prepared to do something about it. Much is made of his youth and his obsession with The Dark Sublime, as if those are reasons to dismiss him, and yet he repeatedly shows more maturity and a deeper understanding of the world than Marianne, who prefers to drown her problems in alcohol.

During one of their early conversations, Marianne reveals to an excited Oli that another episode of the show was written but never shown on TV, scenes from which are revealed intermittently throughout the show. These are, for the most part, played for laughs by Simon Thorp, who’s clearly enjoying himself immensely as the heroic Commander Vykar (and just as much in a brief appearance in the real world as obnoxious actor Bob). So it comes as something of a surprise when the final scene, which brings in the whole cast, gets pretty deep and is ultimately revealed to be symbolic of Marianne’s own personal journey.

Tim McQuillen-Wright’s attractive and intimate set design places us right in Marianne’s living room, although not all the action takes place there. There’s a console cunningly concealed in the coffee table, suitably 70s sci-fi lighting when called for, and a TV screen that doubles as a backdrop when scenes occur elsewhere. This sort of works, although the size of the screen isn’t really sufficient to properly distract us from the stylish decor of the flat and convince us we’re really in the park or a cheap hotel.

The other issue with the play is that at 2 hours 40 minutes it just feels a bit longer than it needs to be. Even before bringing in the deleted scenes from the TV show, there are several plot threads going on – Marianne’s career and her relationships with both Kate and Oli, Oli’s friendship with Joel (who never actually appears), Kate’s romance with Suzanne – and in tying them all up the script begins at times to feel slightly sluggish and repetitive. That said, the closing scene, which references the poem by W.H. Auden that gives the play its title, is rather lovely and feels like a fitting end to the story.

For fans of British TV from the 70s and 80s, Dark Sublime is probably a bit of a must-see, if only so you can sit and cheerily sing along to the Cadbury Fudge jingle before the play begins (yes, I did that). But there’s lots more to recommend it besides nostalgia. This is a rare personal drama about an older gay woman trying to find her place and identity in a changing world, with plenty of laughs – particularly aimed at the world of showbiz – and some interesting questions about the nature of fandom. A bit long perhaps, but still well worth a watch.

Dark Sublime is at Trafalgar Studios 2 until 3rd August.