S3E13 · Full Measure

Complete story — includes the ending

After killing the drug dealers, Walt has a tense meeting with Gus, who makes it clear that his patience has reached its limit. Walt professes not to know the whereabouts of Jesse, who he falsely claims has fled the state. Gus chooses Walt's new assistant, who turns out to be Gale. In a meeting with Gale, Gus says that with his overhead he cannot afford to lose even a week's production. Walt realizes Gus intends to replace him with Gale, the only other trained chemist, and that he will be killed once Gale masters Walt's procedure. Walt deduces that they will have to kill Gale, knowing that Gus will have to keep him, and by extension Jesse, alive once he is the only trained chemist left. As Walt prepares to leave his house to kill Gale, Victor arrives and forces Walt to meet with Mike at the lab. Realizing he is about to be executed, Walt calls Jesse and orders him to murder Gale. Victor races to Gale's apartment to stop this, but Jesse arrives first. After some hesitation, Jesse tearfully pulls his gun on Gale and fires.