The Quagmire Fire was a fire to the Quagmire Mansion caused by an unidentified person with an arson-style Various Fakery Disguise that began in the late evening of August twenty-fifth or the early morning of the twenty-sixth or began on a completely different date in March.
The fire began while the family was at home. Quigley Quagmire was in the library studying a map of the Finite Forest, and describes hearing a shattering of glass and people shouting. His mother ran to fetch him, saying there was a fire, but after being blocked from the front door by smoke, she took him into a corner of the library and hid him inside a secret passage while she left to get his siblings. Quigley recounts hearing the house falling to pieces above him, the sound of frantic footsteps, and the screaming of Duncan and Isadora. He was unable to escape the tunnel , as something had fallen atop the door.
Both Mrs. and Mr. Quagmire perished in the fire, leaving their fortune (the Quagmire Sapphires) to their surviving children. Quigley was believed to be deceased. The Quagmire estate was put under the care of Esmé Squalor until the triplets could come of age.
Brett Helquist tells Lemony Snicket in the letter the sketch is attached to that he "never believed the stories [he read about him], in relation to the Quagmire case or any other." This could imply that Snicket was blamed for the Quagmire fire. What other Quagmire case there could be is unknown, as the Quagmire fire happened sometime after the Baudelaires were in the custody of Monty Montgomery.
It is unclear what the intent of the fire was, but it may have to do with stealing the Quagmire Sapphires from the remains of the fire, although they seemed to be held in a safe place until Duncan and Isadora could inherit them.
Another possibility that it was simply revenge on the Quagmire family, as the fire killed Mr. Quagmire and Mrs. Quagmire. Assuming the Quagmire parents were firefighters (which is only claimed by Jacques Snicket in the books and thus unconfirmed), it could have been an attack by the fire-starting side of the schism.
There are other theories by fans that that Count Olaf also set the Quagmire mansion on fire; in the rare edition of The Bad Beginning, it is said that Olaf used the logs the Baudelaires chopped in his yard to orphan certain students of Prufrock Preparatory School.
Other theories involve Esmé Squalor, who would be put in charge of the Quagmire estate (and potentially Duncan and Isadora) after their parents' deaths, or the Woman with Hair but No Beard and Man with a Beard but No Hair, leaders of the fire-starting side of the schism.
TV Series Divergent Canon
The fire began the night after the Quagmire parents returned from a kidnapping, and Quigley and his mother were drinking cider in the kitchen due to Quigley being unable to sleep. She left him in the tunnel while she went to fetch his siblings, but something fell atop the door, blocking him in.
The fire was set by an unknown arsonist with a Spyglass, causing the source of the blaze to be unknown. While many theorized this could be Esmé Squalor, due to the fashionable outfit, it was later revealed that this outfit was a VFD Arsonist Disguise, leaving the true arsonist ambiguous.
Jacques Snicket said that the Quagmire kidnapping was the result of this, which was the result of:
- a stolen object (possibly Sugar Bowl)
- a moving violation
- a misdemeanor
- two poison darts (possibly the ones used to kill Count Olaf's parents)
- 3 civil suits settled out of court
- a murder
Theories still include Esmé Squalor, as well as the Man with a Beard but no Hair and the Woman with Hair but no Beard, who had abducted the Quagmire parents earlier. Count Olaf is no longer a suspect in this continuity, as he was in Paltryville disguised as Shirley at the time of the fire.
Another suspect could be Georgina Orwell. Nobody knows where she was during the fire, but later she joined Count Olaf in the mill. When Count Olaf came to Georgina's tower, there was a car parked behind him, not recognizable in the dark though. It is aso worth to note that out of people in the Paltryville parents photo Georgina and Quagmire parents were only ones alive at the time with Baudelaire parents perished in fire, Uncle Monty, Ike, Josephine killed by Count Olaf and Larry caught by Olaf's hench people. 
- PROSE: The Slippery Slope
- In the reprise of That's Not How The Story Goes in The Penultimate Peril: Part 2, a copy of the Daily Punctilio on the accident at Lucky Smells Lumbermill is labelled as "LOCAL CITY NEWS AUGUST 25 ACCIDENT AT LUCKY SMELL" with the rest of the words cut off. This confirms that the accident that killed Georgina Orwell occurred on that date. When the Quagmire Mansion is burnt down it is dark, meaning it is either the late evening of the 25th or early morning of the 26th. However, in Season 2, a newspaper reporting that "ORPHANS HAPPY, GETTING SPLENDID EDUCATION" is dated as March, implying the Quagmire parents died in March or it took nearly seven months for the Quagmires to be sent to Prufrock Prep at the same time as the Baudelaires.
- PROSE: The Austere Academy
- PROSE: Lemony Snicket: The Unauthorized Autobiography
- PROSE: The Bad Beginning: Rare Edition
- TV: The Miserable Mill: Part Two
- TV: The Slippery Slope: Part Two
- TV: The Carnivorous Carnival: Part One
- TV: The Slippery Slope: Part One
- TV: The Miserable Mill: Part One
- TV: The Wide Window: Part Two