With every other commuter reading Fifty Shades of Grey, you would be forgiven for thinking discretion had gone out of style, but perhaps it's the thrill of secrecy that fuels the enduring underground swingers community. In the case of suburbanites James and Jennifer, it is also vital to their plan for spicing up their marriage without alerting the curtain-twitching Surrey neighbours.

This juxtaposition of British reserve and hedonistic yearning offers a great opportunity for an Ayckbourn-esque middle-class comedy of manners, and writer/director Andy Moseley takes full advantage of that in the first third of Casual Encounters. There are enjoyable sitcom one-liners, sly observations about seeking refuge in etiquette and some neat visual jokes (swapping the matching cushions in particular) that clearly establish a wearying status quo before it's violently disrupted.

David Scott-Lucas has a lot of fun with James' overeager anticipation and peevish defensiveness, while Sandy Easby's Jennifer is every inch the vexed, put-upon spouse, veering between worrying about dinner arrangements and struggling to rediscover her sexuality. The odd glimmer of vulnerability from both hints at the fact that this seemingly divisive activity could be the last opportunity to salvage a relationship gone stale.

Given the rise of "silver divorces", this midlife-crisis-crossroads theme taps into the zeitgeist, but unfortunately Moseley isn't content to stick with one genre and explore it in satisfying depth. Once the couple's swinging partners are introduced, we lurch into a cheesy crime B movie, and I think finish with a spot of drawing-room farce – all of which is entertaining enough, but sacrifices our emotional commitment to these characters, as well as the chance to dig into the curious code and social structures of this clandestine community.

Sean Meyer, Catherine Houston Eyers and Barry Rocard do their best with stock types, as a wide boy, vamp and doddering policeman respectively, though it wasn't clear whether the slightly cartoonish quality in their performance was intentional or not. The auteur most clearly referenced here, almost pastiched, is Tarantino, but his vivid mix of tones and genres is deceptively difficult to pull off: miss the mark slightly, and you lose tension from the thriller, energy from the farce and humanity from the drama.

Casual Encounters runs out of steam just when it should reach a climax, either with a flurry of comedic activity or revelatory emotional pay-off. A real shame, given the promise in the set-up and interesting range of themes hinted at, such as the current social divide between conspicuous consumerism and embittered entitlement, the role of the internet in changing attitudes to intimacy and sexuality, as well as the inherent risks, and the gradual erosion of real-life communities, exchanged for online approximations.

At an hour, the piece is currently in no man's land between a pithy short and a fully realised play; with further development, its dramatic impact could match its intention. Nevertheless, a game cast makes it a fun addition to this year's Camden Fringe, and a decent part of a wider conversation about relationships in 21st-century Britain.

Casual Encounters, at Etcetera TheatreMarianka Swain reviews Casual Encounters at the Etcetera Theatre.2