An Agatha Christie novel of 1942 (which she dramatised in 1960) presents something of a time-shift problem for the director. Joe Harmston has attempted to find a solution by updating the framing action to 1968 – that year of political and social upheavals – and the second-act flashback to 1948 – as wartime austerity began to soften into something approaching peacetime normality.

It should swathe the whole mystery with a sense of authenticity. It doesn't. The plot itself is an intriguing one; the daughter of a convicted murderess seeks to establish the truth behind her father's death by contacting the five other people who were in the house when he died.

The set itself is an all-purpose one (Simon Scullion) initially behind a gauze. Brigid Guy's costumes should appear to be normal clothes as worn by the well-to-do of both decades, but somehow remain just costumes. There's a soundscape by Matthew Bugg] which comes into its own as we move from London to the south coast, all loud whooshes as though a news photographer's light-bulb was going off at some moment of crisis.

All this stylisation makes it more difficult for the actors to covey the sense that they're playing real people with real lives and the traumas which they bring. Sophia Ward is good as the two Carlas, daughter and mother. Her half-sister Angela provides Sammy Andrews with the opportunity to show us a young woman who has naturally developed from a perky schoolgirl into a young woman content with the life she has forged for herself.

Her old governess Miss Williams is a type which anyone who went to a girls' school in the 40s and 50s will recognise – the dedicated teacher whose influence is never quit shaken off. Liza Goddard hits her off precisely. Then there's petulant society vamp Elsa (Lysette Anthony). I failed to believe in her at either age of her man-devouring career.

The two brothers who cared perhaps too deeply for Carla Crale are played by Robert Duncan as Philip, the abrasive one, and Anthony Edridge as Meredith, altogether a more suave character, even if he does distill some odd potions in his laboratory. Gary Mavers as painter Amyas Carle sketches in the portrait of a man whose art is always going to ride roughshod over people to some effect. As lawyers go, Ben Nealon's Justin Fogg is likeable.