Netflix’s The Dig is a quietly lovely drama set in late 1930s England. It’s got everything a fan of British period films could ask for—gently verdant landscapes, gorgeous sweaters, and characters whose preferred means of conducting tough conversations is via loaded glances. But the movie, which stars Carey Mulligan and Ralph Fiennes and is based on a 2007 novel by John Preston, isn’t just a lush and well-reviewed period piece. It may be a fictionalized tale, but it’s based on the true story of one of the U.K.’s most significant archaeological finds, a discovery that reshaped the nation’s understanding of its history. Here’s what you should know.