There’s a fascinating but rather horrible nature fact at the heart of Morgan Lloyd Malcolm’s 2015 play The Wasp. It concerns the tarantula hawk wasp, which is by all accounts exactly as unpleasant as it sounds. I won’t go into the full gory details – if you want to know more, go and see the play – but essentially the baby tarantula hawk wasp grows up inside the abdomen of a tarantula, eating it from the inside out and only emerging when fully grown. Oh, and apparently it’s got one of the most painful stings on the planet – because it didn’t sound bad enough already.

Thankfully there are no actual wasps or tarantulas in the play (though it seems only fair to those who hate both even more than I do to mention the ones on the wall – which, depending where you sit, are clearly visible throughout). It does, however, feature an equally gripping power struggle between its two characters. The question is: which of them is the wasp, and which the spider?

Heather (Lucy Pickles) and Carla (Rea Mole) haven’t seen each other since school – and there’s a very good reason for that. But then Heather gets in touch out of the blue with a proposition that unhappily married mum of many Carla can’t refuse. She thinks she knows what she’s getting herself into, but with twenty years of bitterness and disappointment between the two women, their reunion is about to take a very dark turn.

The plot feels at times a bit farfetched, but The Wasp’s sting lies not so much in what happens as why. Morgan Lloyd Malcolm, the writer of current West End hit Emilia, obviously knows how to write good female characters – and these two are no exception. We get enough information up front to assume we understand Heather and Carla’s current situations and their history, but as the story gets filled in a little at a time, we realise we’ve barely scratched the surface of what happened between them all those years ago, or the lasting impact it’s had. And while we may not all have gone through the kind of trauma that’s described in vivid, shocking detail in this play, anyone who went to school with other teenage girls can identify on some level with the characters’ experience and emotions, both then and now. (Personally I found that Carla reminded me so much of a girl in my class at school that it was actually a bit disconcerting.)

Presented by The Undisposables and directed by Sarah Fox, the play is set predominantly in Heather’s tastefully middle-class living room; the only hint of the nastiness to come can be found in the aforementioned framed bugs on the wall. As the balance of power shifts back and forth, the twists start to come so thick and fast that eventually we don’t even know who to believe, let alone whose side we should be on. This allows Lucy Pickles and Rea Mole to successfully explore different aspects of their characters; while each starts out as little more than a stereotype based on her social status, by the end of the play the two women have proven themselves to be not only much more complex but also far closer – in every sense – than anyone could have anticipated.

Much like the creature for which it’s named, The Wasp is not a nice play. The story delves into themes of mental illness, domestic abuse and sexual assault, and explores the ways in which human beings perpetuate cycles of violence by passing our own hurt on to others. But it’s also not without an element of hope; for all their differences, the two women do at certain moments reach a kind of understanding, and the whole play hinges on the fact that it is possible to choose kindness over violence. Above all, though, The Wasp is a gripping and suspenseful psychological thriller – so if you enjoy a good twist and a surprise ending, this is definitely the play for you.