Spoilers! Why Netflix's 'The Piano Lesson' might give you the willies

Spoiler alert! We're discussing important plot points and the ending of “The Piano Lesson” (streaming now on Netflix), so beware if you haven’t seen it yet.

“The Piano Lesson” is the year’s most unexpected horror movie.

Malcolm Washington’s directorial debut, adapted from the August Wilson play, has Oscar best-picture prospects and possible acting nominees in John David Washington and Danielle Deadwyler as siblings bickering over what to do with the family piano. But what starts as a deep drama turns into a ghost story as spirits from their past, of hated figures and ancestors alike, make their presence known in an intense, haunting finale.

Malcolm Washington wanted to use supernatural elements as “a kind of Trojan horse" to discuss spiritual belief systems and people's "connections to their lineage and ancestry,” says the filmmaker, younger brother of John David and son of "Piano Lesson" producer Denzel Washington.

Join our Watch Party! Sign up to receive USA TODAY's movie and TV recommendations right in your inbox.

Set in 1936 Pittsburgh, “Piano Lesson” centers on the estranged relationship between Boy Willie Charles (John David Washington) and his sister Berniece (Deadwyler), and their heirloom piano's storied history. In the 1800s, Robert Sutter (David Atkinson) traded two workers of an enslaved family – Boy Willie and Bernie's great-grandmother and her son – to buy the musical instrument for his wife. Later, the siblings' great-grandfather, a woodworker, carved their ancestors' faces and stories into the piano. Eventually in 1911, their father Boy Charles (Stephan James) decided to steal the treasured item from Robert's grandson James Sutter (Jay Peterson).

Boy Charles "said it was the story of our whole family and as long as Sutter had it, he had us. Said we still in slavery," Doaker says of the piano.

Sutter has recently died under mysterious circumstances and his ghost now haunts the piano. He appears first to Berniece, her daughter Maretha (Skylar Aleece Smith) and Uncle Doaker (Samuel L. Jackson) at different times, and in the film’s climax, Sutter’s Ghost attacks Boy Willie and also threatens Doaker’s brother Wining Boy (Michael Potts), Boy Willie’s friend Lymon (Ray Fisher) and Berniece’s preacher love interest Avery (Corey Hawkins). To combat the phantom, Berniece plays the piano and calls on the spirits of her family, who help exorcise Sutter’s Ghost.

The ghost element is in Wilson’s original 1987 stage work “but it was never that pronounced and the ending never really had a final period on it,” producer Todd Black says. “Malcolm really got that down in a way that I don't think anybody has. It's just so surprising and it kind of sneaks up on you.”

Filming the otherworldly scene where Berniece, in a trance-like state, reaches out to her familial spirits, Deadwyler says she doesn’t “necessarily wholly understand or remember everything” but does recall feeling both weighted and weightless. The sequence also transcends the movie for her: “When you have everyone representing the ancestors, they therein become yours. That's what a lot of people have been connecting to (watching the movie), the knowledge that there are people beyond us who are still with us, communicating and trying to ameliorate our lives."

John David Washington recalls watching that as “one of those moments in my career that I'll never forget.”

Another powerful day for Malcolm Washington was when they lined up the actors playing the ancestral ghosts behind Deadwyler in the final cathartic moments before Sutter's Ghost vanishes into flame, saving Boy Willie.

“We made this family portrait that spans space and time," the director says. When "they're all laying hands on her and the lights are flickering, I just felt a collective chill come through all, especially the Black members of our crew. In that way, we transported through the film set back to our story, to our history, the thing that we're trying to connect to.”

Adds Deadwyler: “When somebody puts their hand on your shoulder, it is transformative.”

This article originally appeared on USA TODAY: 'The Piano Lesson' turns into a horror movie at the end. Why?