Here’s an unconventional French Holocaust drama, a film that plays as a guilty remembrance of a dark corner of French history tucked into a ticking-clock thriller.

“Sarah’s Key” stars Kristin Scott Thomas as Julia, a modern-day American journalist investigating the mass deportation of Jews from the Marais neighborhood of Paris in 1942. Some 13,000 French men, women and children were rounded up over two days and stuffed into the Velodrome d’Hiver, an indoor bicycle race track, kept there under cruel and inhumane conditions, and then shipped off to concentration camps. And the entire shameful event was orchestrated and carried out by the French themselves.

Julia, who has married a Frenchman and has a teenage daughter, is consumed with this story — tracking down survivors. But with every new clue, she seems to connect this tragedy to herself — her husband’s family, their modern day Marais apartment.

Director Gilles Paquet-Brenner, working from Tatiana de Rosnay’s novel, balances Julia’s morbid curiosity in the present with the terror of those events as they happened in the past. And as “Sarah’s Key” progresses, we, like Julia, feel the urgency of back then forcing its way into our present day. What happened to this girl and her little brother and will Julia or we ever discover the truth?

Little Sarah was just 10 years old when the police came to grab her family. She pushed her baby brother Michel into a hidden closet and told him to wait for her, then locked the door as she and her family were taken off.

They assume a kindly neighbor will rescue the boy. But Sarah (Melusine Mayance) has seen the anti-Semitism of their neighbors. She becomes consumed with escaping from the velodrome, panicked over how long her brother can survive without her.

The movie is by alternating turns breathless and grimly reflective. Sarah tries to give others escaping from the velodrome the key, and failing that, makes her own attempt. What will Julia find out as she investigates this story almost 70 years later, and how will that impact how she lives her life with the family she has married into? What collective guilt will an entire generation of France carry to its grave?

The performances here are riveting, with young Mayance carrying this story’s flashbacks with brio and urgency. Thomas, ever regal and as at home acting in French as she is in English, makes us care that Julia cares what happened to this girl. The great Niels Arestrup (“A Prophet”) turns up as a farmer who figures into Sarah’s odyssey and Aidan Quinn is another American with ties to the principals.

And Paquet-Brenner never loses track of the narrative, never forgets that this is a mystery, a nervous thriller and a poignant remembrance, a movie driven by its vivid, life-or-death story and the characters who live it. That makes “Sarah’s Key” that rare Holocaust tale that punches through the cobwebs of history and its dry statistics, and brings that terrible past to life.