© David Monteith-Hodge

It's Dougie's 50th birthday, and he's celebrating with his daughter, his nephew, his ex-wife, and her new husband, in their large, plush house with a fancy garden and an actual water feature. Dougie, meanwhile, lives with his mum. The ex, Arlene, congratulates them – mostly herself, really – on making this set-up work; hubbie number two, the suavely groovy Lorenzo, croons "families have changed, man".

This one will have by the end of Douglas Maxwell's play. And they certainly won't be able to play happy non-nuclear families anymore. In fact, things go pretty nuclear, in an explosion of destructive violence that smacks Maxwell being unsure of quite how to wrap things up.

The trouble seems to start when Dougie gives a presentation. He's been contacted by a reparation organisation that tracks down descendants of slave owners and asks for donations, to be given to descendants of people who were enslaved. Dougie is – apparently – the last living relative of Saracen Bell, a slave master. In the grip of an existential crisis about his life having no meaning, he latches on to this idea, and is determined to give the £25,000 he's managed to save for his daughter Molly's university fund away in penance. He needs Arlene's signature to get the money, however.

She goes apoplectic. It might be a scam, he's a credulous idiot, and besides, his own flesh and blood should come first. The play then spirals into arguments between different members of the family, slowly – and rather schematically – revealing that they all have their own dark past, some grubby secret or resentment that's really motivating them as they manipulate each other. Issue of class, race, and responsibility rear up, but the political really turns out to be about the personal – their battles are always about who in the family has the whip hand.

It all goes at a cracking pace, and the writing is sharp, with Arlene especially getting plenty of caustically funny lines. Louise Ludgate plays her beautifully, even when she goes to slightly improbable extremes, but the whole cast is excellent. Richard Conlon's rounded performance as Converse-wearing, craft beer-drinking hipster dad Lorenzo, elevates the part from its potential clichés, while Jonathan Watson emotively captures Dougie's bruised bewilderment at being at the bottom of the heap in life, as well as later suggesting an unexpected stealthy side.

And yet the psychology often feels shaky here - The Whip Hand, although at times seeming to move into heightened comedy territory, also asks us to invest in these people as real, believable characters. But there are too many improbable twists and turns; by the end, character motivations are crumbling like birthday cake. There's something jarring, too, about the reparation plotline – with Maxwell giving Dougie powerful speeches about the true horrors of slavery – becoming just a chip in this family's mind games.

The Whip Hand runs at the Traverse runs until 27 August

Read our full Edinburgh Festival coverage here