Spoiler alert! The upcoming season of the blockbuster PBS series “Downton Abbey” is packed with scandalous plot twists and sensational scenes that are already causing controversy in Britain.

One story line, the traumatic rape of Joanne Froggatt’s character, maid Anna Bates, has produced howls of outrage from fans on the other side of the pond, where the series originates.

Similar concern is expected from Americans following the saga of the English upper class and their servants set in the first half of the 20th century.

“The shock attack scene in ‘Downton’ was harsh and terrifying,” blasts one British critic. “Raped women are not objects to be used to shake up a dull plot.”

Adds another, “Someone might make the point this scene was added to boost falling ratings.

Shame on the producers if this is the case.”

“Ruined the show for me,” a third complains. “I can’t watch the rest of the series.”

But the episode is dark – and incredibly compelling, other viewers say.

Valet Mr. Green, a new character played by Nigel Harman, is seen hitting Bates in the face and dragging her into a room downstairs. Meanwhile, an opera singer’s performance upstairs in the stately home drowns out her screams.

Although the actual assault isn’t shown, Anna emerges from the side room covered with cuts and bruises.  

In addition to the rape horror, another key character will be killed off!

In the season finale, rapist Green dies after apparently stumbling onto a London road – with Anna’s vengeful husband, John Bates, suspected of pushing him.

Believing Green had attacked his wife, Bates was seen leaving Downton on a mysterious errand before the valet’s fatal “accident.”

The latest death comes on the heels of the third season elimination of two leading characters. Downton heir Matthew Crawley, played by Dan Stevens, died in a car crash following the birth of his baby with lady Mary. Meanwhile, Lady Sybil Branson, portrayed by Jessica Brown Findlay, died after childbirth.

Downton Abbey became the most popular drama in PBS history after attracting 12.3 million viewers when its final show of the third season was aired in February.

Americans love Downton Abbey because “we love British accents, and we love the rich history of the British,” says TV critic Bill Mann.

“Many Americans are fascinated with British culture and the Royal Family. There’s so much tradition, and so much intrigue. Downton Abbey portrays the kind of class-based society that is not common in the U.S., providing escapist entertainment without gory car crashes or gunplay. It opens a window into a world that we would never normally see.”

But now the brutal rape scene has many complaining “Downton” has gone TOO far.

Critics charge the show’s creator Julian Fellowes depicts rape in an irresponsible manner – and victims of real-life sexual assaults could be traumatized by watching the episode.

As a result, a warning will be flashed on screen before the episode, the third in the new season that began Jan. 5, reading the program contains “violent scenes that some viewers might find upsetting.”

Fellowes defends the rape story line saying, “The whole point of the way we do things on ‘Downton’ is we don’t do them gratuitously.

“If we’d wanted a sensational rape we could have stayed down in the kitchen with the camera during the whole thing and wrung it out. We’re interested in exploring the mental damage and the emotional damage.”

And Froggatt insists, “I never thought it was going too far. I was surprised when I heard about the story line, but I was really pleased because it’s a really important issue the show is tackling.

“It’s important to remember that for a girl, especially a working-class girl in service, like the character Anna is, these things did happen and happened quite a lot.

“When something is dramatized it provokes a much more emotive response than just hearing a story on the news.”