I’ll be seeing the film next week; this information is from the publicist. The couple saved at least 300 Jews from death during World War II. Here’s a description of the book from Wikipedia: The Zookeeper’s Wife
THE ZOOKEEPER’S WIFE – Synopsis
In 1939 Poland, Antonina Żabińska (portrayed by two-time Academy Award nominee Jessica Chastain) and her husband, Dr. Jan Żabiński (Johan Heldenbergh, a European Film Award nominee for the Academy Award-nominated The Broken Circle Breakdown), have the Warsaw Zoo flourishing under his stewardship and her care.
When their country is invaded by the Germans, Jan and Antonina are stunned and forced to report to the Reich’s newly appointed chief zoologist, Lutz Heck (Golden Globe Award nominee Daniel Brühl of Captain America: Civil War).
To fight back on their own terms, the Żabińskis covertly begin working with the Resistance and put into action plans to save lives out of what has become the Warsaw Ghetto, with Antonina putting herself and even her children at great risk.