- For the symbolic object, see Fly (symbol).
Walt lies awake at two in the morning in his condo, staring up at his smoke detector's flashing indicator light. Later, after he and Jesse scrub the equipment in the superlab, Walt pores over calculations and notes that the meth yields are consistently short. Jesse suggests spillage, evaporation and condensation might account for the discrepancy. Walt rejects these hypotheses, but admits that "the vestiges" left from their cooking process could possibly account for a portion of the missing meth.
After Jesse leaves for the day, Walt becomes distracted by a fly that is loose in the lab. His efforts become increasingly desperate as he chases it all over the room. Walt ends up breaking an overhead lamp with his shoe, which gets lodged in the ceiling. Balancing dangerously on the outer rail of the lab's catwalk, Walt attempts to dislodge his shoe. When Walt tries to swat at the fly with a broom, he falls from the catwalk onto the concrete floor. As Walt attempts to recover, the fly lands right one of the lenses of Walt's eyeglasses.
Jesse arrives at the industrial laundry the next morning to find Walt's Aztek still parked outside. Before exiting his own car, Jesse looks at his ashtray and notices lipstick on an old cigarette butt left by Jane Margolis months before. He places it back, not willing or able to throw it out.
Jesse has to force his way into the superlab; Walt has dramatically increased the air pressure to address what he calls a "contamination". Jesse initially assumes that Walt is talking about a dangerous disease, and is nonplussed when Walt tells him the contaminate is a fly. Jesse works furtively to keep their current batch of meth, halfway through the cooking process, on track. Walt orders Jesse to until the fly is caught, and smacks him with the swatter when Jesse continues anyway. After a scuffle, the fly lands on Walt's head. Jesse, relishing the opportunity to get back at Walt, swats hard. Reeling, Walt crawls on the floor looking for the fly's corpse, but finds only a stray raisin. Jesse convinces Walt that they should step outside and get some air. However, after Jesse passes through the doorway, Walt snatches his keys and locks himself in the lab. Jesse counters by shutting off the lab's main circuit breaker and asking the laundry workers for an axe.
Later on, the power restored. Jesse shows Walt the assortment of pest control supplies he has purchased. Walt deems the nontoxic glue strips acceptable. The partners hang them throughout the lab. Jesse prepares coffee and slips some sleeping pills into Walt's cup in an effort to force him to get some much-needed sleep. Jesse tells Walt the story of an opossum that took up residence beneath his aunt Ginny's house, he continues, but even after it had been removed she insisted it was still there. Ginny would tap on the floor with an umbrella yelling at the opossum to keep it down. Ginny had given the opossum a name, "Scrabbles".
Walt tells Jesse that he's lived too long, struggling through his own guilt and anger, expressing frustration that he cannot make Skyler comprehend his motivation for cooking. Walt ruminates further on when the perfect moment occurred, and reveals he stopped at a bar, where he met Jane's father, Donald Margolis. Walt, becoming groggy, says that earlier the same evening he had been watching TV. On the baby monitor he could hear Skyler singing Holly a lullaby.
The fly begins buzzing again. Jesse wheels over two steel carts, precariously stacks a ladder atop them and starts climbing. Half-asleep, Walt clutches the ladder while Jesse swats. Descending the ladder, Jesse spots the fly and swats. The fly falls to the floor dead. Walt, asleep, misses Jesse's victory.
Later, outside the industrial laundry as Walt's about to drive off, he warns Jesse that if he's skimming meth and Gus finds out, he won't be able to protect him. Jesse denies having taken any. Back at his condo, Walt wakes to the sound of buzzing. Staring up at the smoke detector, he watches a fly land on the blinking light.
- According to creator Vince Gilligan, this was a "bottle episode." Because the season was already "hopelessly over budget," it became necessary to create an episode with minimal production costs. By filming in one location and using the fewest number of actors in the series ever, "Fly" cost substantially less than the average episode.
- This episode aired the same day as the series finale of Lost on ABC, implying that they did not want to compete with the latter show's viewing numbers.
- The filming of the scene where Walt falls from the railing utilized a unique process. A stunt double initially fell and members of the crew took pictures of his landing. Cranston then assumed the same exact position and close-ups were taken of his face.
- This is the only episode in the entire series not to feature Anna Gunn as Skyler. Although there is audio of Skyler singing a lullaby during the teaser, this was simply a reused clip from "".
- Much of the fly hunting scenes with Jesse and Walt mirror Moby Dick, with Walter playing the role of Captain Ahab and Jesse as Starbuck. (With the fly, of course, being the whale.)
- The episode opens and ends (first and last scene) with close-up shots of a fly (also the flashing red indicator light) - coming full circle.
- There was a fly swatter on the table in Tuco Salamanca's hideout, which Walt grabs sarcastically in response to Jesse saying he should hit Tuco over the head with something. ("") Ironically it would be more suitable for the situation in "Fly".
- "Hush, Little Baby" Traditional, performed by Anna Gunn as Skyler (during the teaser)
- "Simplemente Amame" by Cumbre Norteña (in the laundry when Walt has locked Jesse out of the lab)
- "Yo, Gatorade me, bitch."
- ―Jesse cleaning the Superlab.
- Jesse: "Dude, you scared the shit out of me! When you say it's contamination, I mean... I'm thinking like an Ebola leak or something."
- Walter: "Ebola."
- Jesse: "Yeah, it's a disease on The Discovery Channel where all your intestines sort of just slip out of your butt."
- Walter: "Thank you. I know what Ebola is. Now, tell me. What would a West African virus be doing in our lab?"
- Jesse: "So you're chasing around a fly and in your world, I'm the idiot."
- ―Jesse and Walter about the contamination.
- "Look, I like making cherry product, but let's keep it real, all right? We make poison for people who don't care. We probably have the most un-picky customers in the world."
- ―Jesse to Walter.
- "I’m saying I’ve lived too long. I mean–you want them to actually miss you, you know? You want their memories of you to be– But she just won’t–she just won’t understand. I mean–no matter how well I explain it these days, she just has this, this– I mean, I truly believe there exists some combination of words. There must exist certain words in a certain specific order that would explain all of this. But with her, I just I just can’t ever seem to find them."
- ―Walter to Jesse.
- "No, no, no. That was the moment. That night. I should never have left home. Never gone to your house. Maybe things would have…. I was at home watching TV. It was some–some nature program about elephants. And Skyler and Holly were in another room. I could hear them on the baby monitor. She was singing a lullaby. Ah… If I had just lived right up to that moment and not one second more, that would have been perfect."
- ―Walter reconciling a moment in the past.