Season 2 of A Series Of Unfortunate Events is on Netflix as of March 30, but you may already be anxiously awaiting Season 3 and the conclusion of the Baudelaires' tale. Spoilers for A Series Of Unfortunate Events Season 2 and the book series follow. Season 3 will probably introduce Fiona Widdershins, a character who is of importance to Violet, Klaus, and Sunny toward the end of the saga. There was a slight reference to this character in Season 2 that people who have read the books might have caught, so it stands to reason that Fiona will be in Season 3 of the Netflix show. It's possible that the series would stray from the book and show her character beforehand, but it's also possible that Fiona may not arrive until the third episode of Season 3.
Before the Baudelaires can meet Fiona, they need to get out of the incredibly perilous situation that Season 2 left them in. Count Olaf discovers that Violet, Klaus, and Sunny have been disguising themselves as freaks at the carnival. So on the way to the V.F.D. headquarters in the Mortmain Mountains, Olaf tricks Violet and Klaus into riding in the caravan attached to his car. He has the freaks of the Caligari Carnival cut the rope that connects the caravan, leaving Sunny with Count Olaf and Violet and Klaus careening down the mountain.
The next book in the series is The Slippery Slope, and that's where Season 3 will begin, give or take. Fiona doesn't appear in that book; her introduction is in the eleventh book, The Grim Grotto. Since the Netflix series uses two episodes to cover one book, you should expect Fiona to be in the third and fourth episodes of Season 3 — "The Grim Grotto: Part One" and "The Grim Grotto: Part Two."
With A Series Of Unfortunate Events sometimes introducing characters earlier in the show than they appeared in the book, there's a chance Fiona could have a bigger arc and be in the first two episodes of the third season in some way. But it's doubtful that she'll become as significant as adult characters like Jacques Snicket (Nathan Fillion) and Olivia Caliban (Sara Rue). Although, unlike the Baudelaires and the Quagmires, Fiona was raised with the knowledge of the V.F.D. and is a volunteer. She comes in particularly handy after the Baudelaires save Sunny from Count Olaf and then discover a submarine with the V.F.D. symbol on it.
The submarine, the Queequeg, belongs to Captain Widdershins and Fiona is his stepdaughter (so it's debatable if Fiona took her stepfather's last name or not). Fiona is slightly older than Violet and she bonds with Baudelaires instantly — specifically Klaus since the pair of them have a thing for one another. But the young mycologist is also intelligent and she can interpret what Sunny says. The four children eventually head into the underwater cave, the Gorgonian Grotto, to retrieve Esmé Squalor's sugar bowl together. But after that, things turn (what else?) unfortunate.
Without ruining all of The Grim Grotto, the Baudelaires discover that Fiona is related to a very familiar character to them and then something pretty tragic happens due to a betrayal. Because of that, not every fan wants to see Fiona on the show. Yet, it would be pretty shocking if the series chose to leave her out because of the major part she plays in the eleventh book (plus, that Season 2 Easter Egg), so other fans on Twitter have already started their dream casting of the character.
Because of her role in the books, Fiona will most likely join the Baudelaires in their undersea adventures in the third and fourth episodes of Season 3. And Season 3 is already filming. Star Neil Patrick Harris said during a March 28 BUILD Series interview that they've been working on the submarine, so Fiona has probably already been cast. So fans will anxiously (or uneasily) await to see which young actor is announced to be playing this controversial character. And who knows? Perhaps like Olivia Caliban, Fiona Widdershins could end up having a more fan-friendly storyline than she does in the books.