At an auto shop, a mechanic goes over some recent fixes to Walter White's Aztek, including cleaning some residue blood off the grill ("Half Measures") from that deer he had hit (which of course was not exactly a "deer"). He jokes that at least the windshield didn't need to be replaced again. Walt looks inside and finds his pork pie hat in the back seat, which he greets with a smile. Just then he has a thought, he offers to trade his Aztek to the mechanic for $100 and immediately lowers it to $50. The mechanic thinks he's joking, as he's just replaced upwards of $1,900 worth of insurance paid parts. Walter White Jr. too asks his dad to slow down but Walt shrugs it off and trades in the car.
Back at the White Residence, Walt drives home in a brand new shiny pitch black Chrysler 300. Walt Jr., in front of his Chrysler 2006 Chrysler PT Cruiser gives him an uncertain look, politely smiling but clearly not feeling too excited, so Walt trades the PT Cruiser in for his previous new red and black striped 2012 Dodge Challenger. They both beam at each other as they grip their respective steering wheels, elated with their new 'toys'.
At the Houston office of Madrigal Electromotive, Lydia Rodarte-Quayle nervously sits at her desk on a conference call with Germany. She realizes she is wearing mismatched shoes. She receives a tip-off call from Mike Ehrmantraut and seconds later the DEA arrive to question her. She leads them to Ron Forenall who is promptly arrested. Lydia calls Mike to tell him that the methylamine transport will be cut off due to Ron's arrest. Mike informs her he'll send someone else.
At the White residence, Walt and Jr. brag about who would win in a drag race in their new cars while Skyler White silently eats. In the bedroom, Walt gives Skyler $20,000 to launder and she replies that she wants the kids to leave the house for a period of time. Walt shoots down her idea and tells a silent Skyler that he would like a party and chocolate cake for his fifty-first birthday the following day. During breakfast the next day, Skyler forgets to break Walt's bacon into a "51" and Jr. reminds her. She reluctantly obliges.
At the DEA office, Hank Schrader and Steven Gomez go over their diagram of Gus' Drug Empire. They're concerned that no one in prison is talking and that Blue Sky has reappeared on the streets. They believe Mike is their best lead and agree to follow him. The standing ASAC (Assistant Special Agent in Charge) talks privately to Hank and offers him the position of ASAC for Albuquerque. Hank accepts the job.
At a bug bombed house, Jesse Pinkman and Walt break down the mobile lab. Walt asks if he can leave early for his birthday party and Jesse agrees. Walt arrives at home, expecting a party but finds Skyler preparing a store-bought meal.
Hank and Marie arrive at the White house for dinner and chocolate cake. Walt Jr. heads off to drive his new car and Walt gives his sister-in-law and husband a speech about how grateful he is for their support during the rough past year. During the speech Skyler slowly walks deep into the pool and sinks to the bottom. Walt dives in after her.
At the Houston Madrigal warehouse, Jesse arrives to retrieve a barrel of methylamine from a hesitant Lydia. While lowering the barrel, Lydia finds a GPS device attached to the bottom of it.
After getting her out, Marie and Hank suggest Skyler needs psychological help and offer to take Jr. and Holly White for a short time while Skyler gets some rest. Walt agrees after finding out that it was Skyler's idea. In their bedroom, he insults Skyler for being shortsighted. Skyler demands that Jr. and Holly stay away from them as long as they are meth dealers and money launderers. Walt challenges her to tell him how she will stop their kids from staying at their home - "keeping his kids from him". She says she'll hurt herself again, to which Walt counters he'll just be forced to have her committed. Or she'll say Walt beat her or she'll send Jr. away to boarding school. Walt is outraged that she's prepared to let Walter Jr. think he's a wife beater. In desperation, she tells Walt that she isn't as good at coming up with these plans as he is, that she's at a loss, just a coward and that all she can do is bide her time. "Bide you time? - Bide your time for what?" asks Walt rather bewildered, wary of the answer. "Wait until the cancer returns," she blurts back at Walt, looming over her as she cowers on the bed.
The next morning, Walt receives a call. Jesse tells Mike about the GPS device and Mike, thinking it too sloppily done to be the DEA, believes it was Lydia attempting to get out of their business. Mike prepares to leave to kill her, regretting having given her a chance already, but Jesse stops him and insists they vote on it. Walt tells them that the cooks must not stop under any circumstances, and that they're only just beginning.Mike's not happy stating she's a liability who will get them caught.
In the parking lot, Jesse compliments Walt on his good idea, presumably, of how to deal with Lydia. Jesse gives Walt a brand new TAG Heuer Monaco Chronograph watch and wishes him a happy birthday. At home, Skyler smokes again, using Walt's birthday mug as an ashtray. Walt tells her the children are staying away another day. He then tells her about the watch and how Jesse wanted to kill him a few weeks prior, but came around. He tells her she'll come around too.
Walt falls asleep to the watch's ticking, which escalates to almost the sound of a gun chamber revolving.
- The episode title appears to be a reference to the age of Walter White, 51. It could also refer to the fact that the balance of Heisenberg/Walter White is teetering.
- The number "51" can be seen on the mug Skyler is using as an ashtray late in the episode.
- The watch that Jesse gives Walt is the Tag Heuer Monaco, a watch forever linked to and made famous by Steve McQueen in the movie Le Mans (1977). Steve McQueen died of a rare, inoperable lung cancer.
- The loose thread on Walt's hat could be a foresight that the Heisenberg empire will fall.
- The ending scene of the episode with Walt's watch ticking is almost a metaphorical meaning that his time is running out.
- Walter puts the watch on Whitman's Leaves of Grass book.
- Saul Goodman does not appear in this episode.
- This is the fiftieth episode altogether, and Walt turns fifty-one.
- Jr. gets the same type of car (Challenger) as he did in Season 4, episode 6.
- Walt says that Marie and Hank are watching Ratatouille. Somewhat humorously, the film is based on the irony of a rat becoming a chef. This, along with the character Gusteau's famous motto in the film "Anyone can cook!" could be seen as poking fun at Walt's uncharacteristic decision to cook meth in Pilot.
- During this episode Walter said the following line: "The Methylamine Keeps flowing, no matter what... Nothing stops this train" Which can else foreshadow next episode (Dead Freight) train heist.
- Hank: "What about that Lydia what's-her-name? Lady Banjo-Eyes at the warehouse?"
- Gomez: "In this world? No way. Too uptight. Too together."
- Hank: "Maybe. She was wearing mismatched shoes. How together can she be?"
- —Hank and Gomez discussing Lydia's involvement.
- "Sorry, but I'm not gonna apologize for being careful - with all that's been happening, for all I knew you were one of those undercover people they send into high schools, so, yeah, I'll take paranoid any day over getting gang-raped by prison guards."
- ―Lydia talking to Jesse.
- Walter: "You didn't set out to hurt anybody. You made a mistake, things got out of control, but you did what you had to do to protect your family and I’m sorry, that doesn't make you a bad person. It makes you a human being."
- Skyler: "I don’t need to hear any of your bullshit rationales. I’m in it now, I’m compromised, but I will not have my children living in a house where dealing drugs and hurting people and killing people is shrugged off as ‘shit happens!’"
- —Walter and Skyler arguing.
- Walter: "Wait for what? What are you waiting for?"
- Skyler: "For the cancer to come back."
- —Walter and Skyler arguing.
- Mike: "You don't know this woman like I do. I had a chance to deal with this before, and I gave her a pass. That's what I get for being sexist. Now if you'll excuse me..."
- Jesse: "Mike, you can't, just—Look, that's our precursor. We need her."
- Mike: "Kid, if we have to ramp down for a while, so be it. It beats working with a lunatic who's gonna get us arrested or killed."
- Jesse: "Look, she didn't seem crazy to me, you know? She just seemed, like, uptight."
- Mike: "And now you're being sexist. Trust me, this woman deserves to die as much as any man I've ever met."
- —Jesse and Mike discussing Mike's plan to kill Lydia.