Exactly what that bang is, we're not going to say, in deference to the maybe half-dozen "Downton" fans who still don't know the shocking truth.
The larger point remains that after Sunday's "Masterpiece Classic" (airing at 9 p.m. on PBS), viewers must suffer "Downton" withdrawal until next season.
But until then, we'll have our memories.
And what a season this has been. The beloved valet Mr. Bates was sprung from jail and a trumped-up murder charge to begin married life with his bride, the plucky lady's maid Anna.
Robert Crawley, Earl of Grantham, has gotten Downton Abbey back on its feet financially with an able assist from his son-in-law and presumptive heir, Matthew Crawley.
Matthew wed his true love, Lady Mary Crawley. But another of Robert's daughters, Lady Sybil, died tragically during childbirth.
Through it all, Robert's mother Violet, Dowager Countess of Grantham (played by the sublimely scene-stealing, Emmy- and Golden-Globe-winning Maggie Smith) delivered a barrage of withering, hilarious rejoinders to virtually every narrative twist.
"I remember my very first scene with her in Season One," says Hugh Bonneville, who plays Robert, lord of the manor. "She's complaining about the new electric lights, and suddenly she put her fan up to her face to shield herself from 'the glare,' and spent the entire scene like that. It was so funny, and I was just, 'All right! There's no point in my even being here. She's just marched off with the scene!'"
Now, as then, "Downton" is a plush, penetrating peek into the lives of the aristocratic Crawley family and their household servants in an English castle of a century ago. With a cast that also includes Michelle Dockery, Elizabeth McGovern, Dan Stevens, Jim Carter and Brendan Coyle, the series this season has drawn an average 11 million viewers each week while spurring another surge of "Downton"-mania, even from first lady Michelle Obama, who pulled strings to get episodes of the new season before it premiered.
"Downton" has even been parsed for its political underpinnings. Last month, Fox News host (and native Brit) Stuart Varney declared that "Downton" celebrates rich people, who "in America today are reviled. They're dismissed as fat cats who don't pay their fair share."
Yet on "Downton" the rich people are "generous," "nice," "classy" and "they've got style," Varney said, "which poses a threat to the left, doesn't it?"
It is rare when public television is accused of threatening left-wing orthodoxy. But "Downton" has a way of engaging people, both the 99 percent and the 1 percent alike.
And, yes, as the wealthy, patriarchal Lord Grantham, Bonneville does indeed exude classiness and, at crucial moments, generosity.
But that's not the whole picture. Robert Crawley is also confounded by the modern world of post-World War I as it upsets the social hierarchy.
"I don't think I'd have a huge amount in common with Robert if I met him at a dinner party," Bonneville said. "But I like the guy. I like the fact that while he does bluster, and he's pompous sometimes, and he makes mistakes, there's a decency and a love for his family underneath it all."
Impeccably clad in a three-piece gray suit and pink tie for this recent interview, the 49-year-old Bonneville looks to the manor born.
Nonetheless, he brands himself a member of the British middle class, and his roles have strayed some distance from the lofty likes of Robert Crawley.
For instance, Bonneville has been affable in "Notting Hill" and "Mansfield Park," and downright villainous in "The Commander."
And coinciding with his "Downton" duties, he also played the addled Head of Deliverance for the Olympics commission in "Twenty Twelve," a riotous BBC miniseries that spoofed preparations for the London Olympics.
"There are people who think I've been doing nothing for 25 years, and then suddenly I get this role on 'Downton Abbey,'" Bonneville said. "But I've had a really lovely time for 25 years! I've played everything from Shakespeare to sitcoms to period dramas to modern serial killers. I consider myself a character actor, and I do love playing different instruments in the orchestra when I get the chance."
"This is one of the few settings, alongside a hospital and a police station, where you can legitimately find a real cross-section of society under one roof," he said.
"But underneath it all, this series is about romance rather than sex, it's about tension rather than violence, and it's about family -- both the literal family and the staff as family. It explores the minutiae of those social structures, the nuances of the system as to whether someone's in or out."
"These days," Bonneville said, "we have relationships that are forged, consummated and brought to an end within 24 hours. Back then, the pace of life was slower, and I think we like to breathe out and enjoy that world -- albeit for only an hour or so, on a Sunday night."
Just one more Sunday night, for now.
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