If a writer turned up at a Hollywood studio with a script about a bunch of people who escape the town villains by living in the sewers, they'd be turned away at the door and told to come back with something more realistic.
Except it is real. In Nazi-occupied Poland, Leopold Socha - not a heroic figure by any account - was a simple man who used his knowledge of the city Lwow's (now Lvov in the Ukraine) underground tunnels to shelter hundreds of Jews from their persecutors.
It is one of many wartime stories of heroism handed down through the generations since, and now it's been turned into a haunting Oscar-nominated film, In Darkness, directed by Polish veteran Agnieszka Holland.
Although Holland hadn't heard Socha's story before she received the script, she explains: "I knew a lot of stories from that period, reading and talking to people for years. There were many stories of others who'd risked their lives to save perfect strangers, as well as of people who did the most terrible things. I was born after the war, but the war was very present."
As well as the practical challenges of keeping a tale based mostly underground accessible and interesting, Holland had the extra burden of eschewing dramatic devices for the sake of history:
"It's a huge subject. You're painting a picture of humanity, and asking questions which we don't really know how to answer. In another film you have the luxury of making tiny little decisions to improve the bigger picture, but with something like this, you have to stay true to what you believe is right, you can't get away with anything just to make a better movie."
The film, which Holland worked on for five years in all, has been the most successful this year at the Polish cinema, and Holland has been touched by the reception it has received, particularly from descendants of those who tucked themselves away in the sewers.
But her biggest sentiment is reserved for Socha himself, a man untroubled by good conscience or awareness until he found himself in extraordinary circumstances and, like the far more famous Oskar Schindler, moved to help.
"It was extraordinary how he can suddenly become responsible for these people he doesn't even like very much." reflects Holland.
"It almost happens against his will and without his knowledge, and that I found very moving. I don't want to make films about heroes, because they are very brave or epic, what interests me are the people in the street, because we can so easily project ourselves onto them."
In Darkness is in cinemas now. Here's the trailer ...