*SPOILER WARNING: THIS IS A COMPLETE OVERVIEW OF SEASON 4 OF BREAKING BAD*

When last we left our hero, Walter White had a gun pointed at his head, Mike on the other end, ready to fulfill his orders to off Walter in order for boy scout Gale to take over the lab. The wrinkle in the plan? Jesse is on his way to Gale's apartment, his own gun in hand, ready to kill the only obstacle in the way of Walter and Jesse staying alive and staying employed. The closing seconds of the Season 3 finale, "Full Measure," saw Jesse aim the gun at Gale, tears in eyes, and pull the trigger as the screen goes to black. The question: did he really shoot Gale? Did he kill him? The answer, as most fans figured, was no.

In the Season 4 premiere, "Box Cutter," the question was almost immediately and undoubtedly answered: yes he did. Unflinching, unblinking, the series killed off another innocent bystander in the Walter White Game of Meth. The body count keeps rising, and only continues to rise as Gus henchman Victor decides to offer himself a promotion by revealing to Walter, Jesse and Mike that he can cook the amazing blue meth Walter and Jesse concocted in a run-down RV oh-so-long ago.

Gus comes to the lab as a begging, pleading Walter fights for his and Jesse's lives. It's in this moment that the bond between Walter and Jesse reaches a new height. In his sad, twisted, deteriorating world, Walter has nothing but love and loyalty to Jesse Pinkman. Maybe it's misguided, maybe it's almost gotten him killed on many occasions, but Jesse was all he had when this started and he has sent Jesse through hell. Death, murder, kingpins, threats, beatdowns. All because of Mr. White.

Gus's plan doesn't include killing Walter or Jesse. Calmly, he removes his outer clothing, dons a hazmat suit and proceeds to tear the throat out of Victor with the episode's titular box cutter. No remorse, no emotion, no regrets. What's done is done and not only cannot be undone, doesn't need to be undone. Gus believes in Walter White for now.

The chess game begins.

Walter becomes obsessed with offing Gus Fring, but at each chance, he's pushed back. In "Thirty-Eight Snub", Walt buys a snubnosed revolver in the hopes of finding an opportunity alone with his rival, but after mentioning this to Mike (the always fantastic Jonathan Banks), Mike punches Walt, seemingly to knock some sense into him. Whether or not it's meant to toughen Walt and push him in a proper direction to killing Gus remains to be seen.

Jesse spirals out of control after shooting Gale. He purchases the best stereo system money can buy, invites his many drug-addict acquaintances (is there such a thing as a drug-addict friend?) to his place and begins a never-ending party. The noise, the pounding thump, the distractions, they only serve as a band-aid. When things get quiet, Jesse falls apart. In "Bullet Points", Mike clears the party and kidnaps Jesse, but Jesse doesn't care. It's only as they keep driving in Mike's car that Jesse's dead-inside emotions subside and he realizes he could die. But it's Gus that orchestrates Mike "babysitting" Jesse, becoming unlikely partners. Mike could care less about Jesse, but Gus sees Jesse as another chess piece. He knows Walt can't be trusted any more, so he needs Jesse on his side soon.

Through all this, Skyler has submitted to the fact that Walter is in a dangerous game and tries to do what's best for the family. She buys the car wash where Walt had been working part-time in order to properly launder the drug money.

After Hank's harrowing escape from The Cousins, he's been left a broken man, unable to walk on his own. He turns to an unlikely fascination with minerals, but when Marie returns to her old ways of kleptomania, he breaks out of his funk and becomes engrossed in Gale's murder. How was Gale involved? Who killed him? And why did the vegan have napkins from Los Pollos Hermanos, a fried chicken joint? He connects the dots but no one else is bothering to connect them with him. His decision to closely follow Gus Fring, Los Pollos Hermanos and the industrial laundromat that also houses the meth lab ends up putting the final nail in the coffin between Gus and Walter.

In "Hermanos", we're introduced to a portion of Gus Fring's story. In a flashback, he and his business partner, Max, attempt to go into business with the Mexican drug cartel and kingpin Don Eladio. Ever-present in this scene is Hector Salamanca, the present-day wheel-chair bound uncle to Tuco and The Cousins. Max pleads their case to Don Eladio, who is affable and fun-loving, but at his command, Hector shoots and kills Max as a warning to Gus. This trigger, so to speak, sparks a deadly vendetta against the Mexican drug cartel that has fueled Gus to the present day.

After Hank bugs Gus's car and comes up short, Walter decides, in "Bug", to also bug Jesse's car, to see if he has actually been near Gus. Jesse denies it, but Walt knows he's been to Gus's house and can't figure out why he hasn't tried to kill Gus with the ricin Walt gave him. Jesse can't figure out why Walter knows this and when Walt reveals he had bugged Jesse's car, the two engage in a knock-down, drag-out fight for the ages, ending with Jesse telling Walt to leave and never come back.

In "Salud", Gus, Mike and Jesse head to Mexico to align with the cartel... and hand off Jesse as their cook. Mike assures Jesse that either all three will leave together or none will leave. After producing a top-notch product, the trio celebrate with Don Eladio and his gang, complete with an expensive bottle of tequila. So expensive, it's deadly. Gus ingests an antidote before taking a drink to encourage the rest, including Eladio, to partake. After vomiting back up as much as he can, Eladio and his crew drop like flies, but the effects linger on Gus as Mike and Jesse get him out of there. Hector's grandson, Joaquin, opens fire on our boys, hitting Mike, but all three escape with their lives.

The final three episodes play out like an excellent, tense film. "Crawl Space" puts Walter and his family in grave danger, as Gus effectively fires Walt and threatens that he will kill Walter's family if he intervenes in his own plans to kill a snooping Hank. Walt's plans to disappear forever in exchange for saving Hank are ended immediately when he discovers he doesn't possess the $500K needed for the job. Skyler has given Ted Beneke over $600K to pay back taxes which would end up shining a light on Skyler, and Walter. So begins the descent into madness for Walt as he's screwed from all angles. One last screwjob from Beneke.

"End Times", a shining achievement for Aaron Paul, who won the Emmy for this episode, takes us on the final showdown between Walter White and Gustavo Fring. It's here that everything is established: one will live, one will die. Walter stays in his own home while his family stays with the Schraders. He sits in his backyard, spinning his snubnosed revolver on the table. It stops multiple times with the barrel pointing at him. On his last spin, it stops on a plant. A seemingly pointless image for the viewer.

Meanwhile, Jesse's girlfriend's son, Brock, is poisoned, leaving our two main characters feuding once again as Jesse demands that Walter admit he poisoned the child. Once cleared heads prevail, they realize Gus is behind the sinister development and both vow to exact revenge through death. Jesse lures Gus into the hospital for a one-on-one, while Walt rigs up a car bomb to take out Gus once and for all. But the episode ends as Gus senses something amiss, while Walter watches closely from a nearby rooftop. The plan is foiled and Gus leaves, unharmed.

Gus remains in play with his king, queen and key pieces in play. Walt's only left with pawns and an impending checkmate. Or is he?

"Face Off" boasts so many iconic, memorable moments for a series striving to be remembered as one of the greatest TV shows of all time. An unlikely alliance forged between Walter White and Hector Salamanca. A pulse-pounding scene in which Tyrus searches Hector's room before Gus arrives, while Walter waits just outside the window. Gus's slow-motion stroll into the retirement home with Apparat's appropriately-titled Goodbye playing in the background. Gus's reaction to realizing it was all a ploy as Hector repeatedly rings his wheelchair bell and... BOOM. Finally, Gus exiting the room, seen from only one side, as he calmly adjusts his tie. What we don't see right away is that half of his face is missing as he falls to the floor. Dead. Finally.

Hence, "Face Off".

Most shows would be content with such a high-profile send-off for a season. Heck, it could have been a series finale. But even as the dust literally settles, we are treated to one last, heart-breaking fact: Brock was not poisoned with ricin after all. It's a plant called Lily of the Valley. And as the season closes, we're shown the exact plant in Walt's backyard that the gun had landed on, triggering Walt to do the unthinkable: he poisoned a child to get what he wanted.

Walter White's descent into madness is only exceeded by his descent into pure evil. He started out a hero. A spokesperson for the everyman schlub, toiling away in nothingness, living out his latter years by just being alive. He broke free from his life, his death sentence, his everything, and he became a meth cook. But then he became bad. He let an innocent girl die. His brother-in-law was irreparably damaged by his actions. He poisoned a child, not with the guarantee of survival, but with a hope that he would save himself, even if it meant a child's death. His actions are a runaway train, going faster and faster, the brakes long gone, and a wall up ahead. There's no stopping it. But there's also no stopping Walt.

Walter knows what wrong is and he chooses it without thought now. He has become the evil he had claimed to be battling. He is the villain.

He is the one who knocks.