Somewhere in Essex, on the muddy banks of the Thames, two boys are hiding from the police. Charlie and Wayne are jubilant, elated. They have “actually dared to do something” at last, though what they have done, exactly, we don’t know yet. They’re panting from the chase and the adrenalin rush and shouting with excitement – until Jake arrives.

Jake’s late, they lost him, they thought he’d gone home. What’s wrong with him? He is nauseous and terrified, and slowly the night just gone begins to unravel before us as we see what brought them here, to this beach that’s not really a beach, where they are stuck, trapped like rats and turning on each other.

If I’ve made Mudlarks sound, so far, like more of an actual living experience than a play, that’s because Vickie Donoghue has written an incredibly absorbing piece of drama, at its best during moments of horrible realism and well aided by Amy Cook’s stunning set. The stage floor is covered with real mud that sticks to the actors’ knees and backs when they crouch or fall, and Cook’s attention to detail is fantastic. The shopping trolley half-sunk in mud looks like it could really have been there for years.

This made the decision to stage the play in traverse rather a strange one for me. You only had to look up to see the other half of the audience sitting opposite, looking back at you, which broke me out of it at times. I couldn’t work out if Director Will Wrightson actually wanted us to remain aware that we were watching a play – but why? For what purpose? Perhaps he wanted to remind us that we, as a society, have a responsibility to boys like Charlie, Wayne and Jake, but personally I found the mixing of high-realism with non-naturalistic elements rather jarring. A stylised imagined boat-trip, for instance, towards the end of the play, though beautifully lit and performed, seems to come from nowhere and left me similarly puzzled.

In spite of a few slightly confusing directorial decisions, the performances are all very strong, with James Marchant as Charlie particularly noteable and slightly terrifying. His eyes seem to glimmer with malice, but he’s far from being some kind of pantomime villain and is played with huge depths of sensitivity and understanding – though Marchant does, it must be said, look about a decade away from being the ‘16/17’ the script describes. Despite arriving last, Scott Hazell is arguably the lead and certainly the moral compass of the play as Jake (all of which is played upon nicely in the latter third), as well as hugely believable throughout.

As Wayne, Mike Noble tackles what seems to me the most difficult part in the play. Often the comic relief, he is the most overtly likeable character of the three but also utterly complicit in the morally bankrupt act at the play’s core (I won’t tell you what it is – the reveal is well-done), and Noble does a good job of turning this dichotomy into a cohesive performance. However, Wayne feels at times, with his innocence and his sense of humour, as if he is from a different time, place and play altogether. His reminiscences of mischief from days of yore is so utterly removed from what he is doing now – he tells a story, for instance, about being given a week’s detention for putting a whoopee cushion on a teacher’s chair – that it is as if Dennis the Menace has suddenly become a young offender. Wayne is also constantly backwards-looking in a way that feels a little contrived. He’s not 70; who, at seventeen, is so obsessed with their own childhood? It feels as if Donoghue has made him entirely responsible for her audience understanding the relationship between the three boys and their backstory. She tells rather than shows us that they have grown up together, which is a shame, because the interplay between them is well-achieved in so many other ways.

Ultimately, this telling-not-showing is the main problem in Mudlarks. Donoghue sometimes lets the message get in the way of the drama, and while it is an important one – that in our class-divided society, there is no hope of a real future, no hope of escape for boys like these – it is weakened by making the characters tell us that this is the point. “We stay”, Charlie says at one point. “Get a girl pregnant. Get a shit job and we stay.” Donoghue doesn’t need to tell us this. Her writing is strong enough throughout most of the play that we could construe it, and she needs to trust both herself and her audience more.

Mudlarks may not quite pull together into a truly remarkable piece of theatre, but this is Donoghue’s first play: there’s still a lot to love here. She’s definitely one to keep an eye on and at its strongest moments, Mudlarks is, in spite of its problems, brilliant.

Mudlarks is playing at the Bush Theatre until 20 October. For more information and tickets, see the Bush Theatre website. Don’t forget that U26s get £10 tickets.