If you still haven't seen the episode - and have managed to avoid spoilers up to this point, somehow - then do not read on any further. Because while there was plenty of inconsequential stuff in the instalment, the one big event is something that we just can't ignore.
Perhaps we should have seen Lady Sybil's death coming; Jessica Brown Findlay is becoming a big star and it was a surprise to see her in this much Downton. But that doesn't mean that it wasn't hugely affecting - and all the more so because we had no real idea that it was about to happen.
In this day and age, when everything is signposted with spoilers and hints, it was wonderful to be surprised by Sybil's untimely passing. But the episode did a reasonable job of keeping it hidden, too. Of course there was foreshadowing - we kept getting told at the start of the episode how healthy Sybil was, which is never a good sign.
And apologies to Dr Clarkson, but Robert wasn't the only one who wondered about his judgement as a doctor; before the show even flagged it up, I was muttering about Matthew's misdiagnosed tingles. Naturally, it quickly becomes clear that Clarkson's the one we should be siding with when he warns of Sybil's deteriorating health; Sir Philip, a knighted gynaecologist called in by Robert, is such a pompous prig that he's obviously not going to be proved right.
It's actually distressing seeing Sybil in labour - Allen Leech does his best work of the series in this episode, and was great as Sybil slipped into delirium. But the show does bluff us all when she welcomes a healthy baby daughter and everyone feels that they can relax and celebrate (as Clarkson fumes silently).
But, of course, things aren't that simple - and in the middle of the night (accompanied by typically absurd and over-the-top Dramatic Music) - Sybil becomes seriously ill. This scene is just absolutely devastating to watch, as the actors are actually given stuff to prove their chops. Amidst all the drama, it's almost entertaining to see Clarkson put on his 'I told you so' face, but overall it's just really upsetting.
Again, Leech is fantastic, as is Elizabeth McGovern, who desperately clings onto her young daughter. But everyone is absolutely brilliant, whether it's Matthew's resignation as he leans against a bedpost, Mary's stoic lip-quiver, or Edith's look of horror. Even the hardest of hearts would be moved by Sybil's death, and it's actual drama from a realistic place, instead of the often insane plot twists. It's not like women don't die of childbirth, and didn't a lot in the 1920s.
As is often the case, Downton's little touches were wonderful: the staff standing in shock being told the news; Thomas showing a human side by sobbing over one of the few people who has been kind to him; Violet arriving at the house and having to take a moment to steady herself, looking like an old woman for pretty much the first time.
And the death was not just a death - it appears that there are going to be consequences for some time. Cora is furious - she's just lost her youngest daughter - and she's taking it out on Robert, convinced that he's to blame as he refused to listen to Clarkson's warnings. She's wonderfully calm and passive aggressive about it all; the first hint of her anger comes when she asks Mary to tell Robert to sleep in the dressing room - heartbreaking in itself, as she's talking to Sybil's lifeless body: "You are my baby, you always will be. Always my beauty, my baby."
But she becomes much more explicit the following day, when she announces that she is going to write to Clarkson to apologise: "If we'd listened to him, Sybil might still be alive, but Sir Philip and your father knew better and now she's dead." I mean, ouch - she even refers to Robert as "your father". But you can't blame her for her devastation, and you feel sorry for Robert too, who obviously feels horribly guilty (even though Violet tries to soothe him in a moment of sweetness). Elsewhere, it's a bit teary seeing Edith and Mary hug, even though Mary acknowledges that this doesn't mean they're going to like each other now.
Matthew's in the doghouse, too, after trying to sort out the estate just the day after Sybil's death (hey, Murray's here! It's convenient!). He's caught by Mary, who's understandably not too pleased with him (plus, there's the hint that he and Mary might not be able to conceive after his wartime injury). But naturally, the consequences will be felt the keenest by Tom and his newborn daughter, which is why the final shot of the duo at one of the windows in Downton's huge edifice is just so affecting.
Compared with all of this, then, it's hard to even care about the rest of the action, although it was all entertaining enough. Ethel is now working for Isobel Crawley, who is always so well-meaning that it's actually just infuriating. Still, there's some comic relief as Ethel attempts to make a kidney soufflé (which sounds vile to begin with) and messes up tea by putting honey in it. There's a little social commentary too, as Mrs Bird quits in protest at working with a prostitute, and Carson does his inevitable huffing and puffing.
Elsewhere, the writers have remembered that Thomas is gay and with a bit of pushing from evil O'Brien, he starts becoming "overfamiliar" with Jimmy. The best bit is when he helps him wind a clock and gets all up close, murmuring about warming it up in the morning. I mean, I know Downton's been getting a bit saucy lately, but someone get me a fan. Anyway, it's bad news for Thomas, as Jimmy's not feeling too comfortable - this is going to end badly for one of them.
In fact, Jimmy's involved in a rather uninteresting love triangle in the kitchen - Daisy likes Alfred who likes Ivy who likes Jimmy. There'll be tears before bedtime, especially if Daisy keeps being so mean to the poor new kitchen maid, who's just trying to settle in. Mean, mean Daisy.
Meanwhile, in amidst all the crying about Sybil, Anna and Bates are feeling smug because Mrs Bartlet saw that Vera had pastry under her nails on the day she died, meaning that she must have cooked her poisonous pastry herself. Of course, they have to get Mrs Bartlet to say that without her knowing that it could save Bates - unfortunate, as vaguely evil prison guard and vaguely evil prisoner have teamed up to sabotage Bates and have already warned Mrs Bartlet (I still don't know what Bates has done to deserve all this hatred, except maybe just being annoying).
In other news, Edith gets offered a newspaper column, but as always she's overshadowed by her sisters - this time, when one of them selfishly decides to pop her clogs. But really, that overshadowed the entire episode - looking back at it, it's hard to focus on anything except Sybil's face-crunchingly sad goodbye. And no doubt, there's plenty more emotion where that came from...
Downton Abbey airs Sundays on ITV1.