Directed by Gilles Paquet-Brenner. Starring Kristin Scott Thomas, Mélusine Mayance, Niels Arestrup, Frédéric Pierrot, Dominique Frot, Michel Duchaussoy Club, QFT,Belfast; IFI, Dublin, 111 min

THE HOLOCAUST was, surely, sufficiently catastrophic to require little melodramatic enhancement. Well, Gilles Paquet-Brenner thinks differently. The director has shunned no cheap tricks while turning Tatiana de Rosnay's bestselling novel into a pounding, cliff-hanging, sentimental potboiler of a movie. Sarah's Keyis as watchable as a mid-ranking John Grisham adaptation and has about as much intellectual fibre.

Wearing her bilingual robes, the reliably flinty Kristin Scott Thomas turns up as Julia, an American journalist, long resident in Paris, investigating the deportation of French Jews during the second World War. In the course of her inquiries she discovers that the recently refurbished flat owned by her husband’s clan was previously occupied by a Jewish family.

There’s more. When the original owners were captured, the family’s young son was left locked behind a hidden door. His sister Sarah hangs on to the titular key and, while imprisoned in the Paris Velodrome and, later, in a detention camp, she yearns to get back and set the child free.

Back in the present, Julia, now pregnant, wonders whether to tell her in-laws how they came into possession of the property. Meanwhile, the threads of Sarah’s story weave themselves together. Perhaps she’s still alive somewhere.

Sarah's Keydoes have an irresistible narrative drive. Various mysteries are expounded and each is unravelled at a steady pace. The shots of wartime Paris are lavish and the actors manage to treat even the cheesiest dialogue with some respect.

But the film is wounded by its clumsiness and its addiction to airport-novel storytelling. A group of young people, colleagues at Julia’s magazine, are on hand to ask stupid questions, so that the heroine can painfully explain 20th-century history to an increasingly patronised audience. The plot is gaping with holes and the final denouement is as drippy as it is unlikely.

There are pleasures here, but they’re mostly guilty ones.