Agatha Christie can always be relied upon to deliver solid storytelling, with vintage charm, a gripping conclusion and possibly a twist in the tale.

This wonderful co-production of Frank Vosper’s adaptation by Fiery Angel and Derngate Northampton, delivered on all counts.

It starts slowly – too slowly perhaps – with some mannered chit-chat and Hyacinth Bucket-style keeping up of appearances in an entirely believable pre-war domestic scene of upper middle-class manners of petty snobbery in Bayswater.

The young Cecily Harrington (Helen Bradbury) breezes in like a breath of fresh air, but is clearly perturbed.

Despite having won a fortune in a sweep stake, she is suffering jitters over her forthcoming marriage to fiancé Michael (a suitably stodgy yet dapper, respectable and dependable-looking Justin Avoth).

Michael has been serving in the Sudan and despite their engagement the pair have been strangers for years.

A frisson materialises in the shape of adventurous world traveller Bruce Lovell (played with believable charm and impeccable North American accent by Sam Frenchum).

Cecily falls in love, breaks off her engagement, decides to sell the flat and marry the stranger. And that’s where it gets exciting.

The longer second ‘half’ is hugely enjoyable, and we are led to build our own conclusion as the obvious begins to dawn. But how will it play out?

Bradbury is the stand-out star, entrusting Cecily with an adorable sweet, trusting nature – but, as we’d hope in this day and age, a brighter intelligence, cooler composure and more grit than we might have expected.

Avoth is great as the mysterious stranger and equally cagey husband and Crispin Redman as the criminology-obsessed GP.

Praise should also go to director Lucy Bailey and designer Mike Britton for a slick sliding set which subtly re-frames each scene and nudges the tale along.

TIM HUGHES 4/5