Walter White's chemotherapy side effects begin to show at school and during cooks, and Jesse discovers the truth about Walt's cancer when he spots the radiation targeting mark on his chest. When Jesse's attempt to negotiate a distribution deal with violent drug lord Tuco Salamanca ends in a severe beating and stolen product, Walt shaves his head, adopts the alias Heisenberg, and walks into Tuco's hideout alone armed with fulminated mercury. He detonates it, takes fifty thousand dollars, and secures a wholesale deal: two pounds a week, cash upfront.

This episode marks the point where Walt stops reacting and starts acting — the Heisenberg persona is no longer a coping mechanism but a deliberate identity. The deal with Tuco reframes the entire operation's scale and danger, and an innocent janitor sits in county jail for Walt's crimes while Wal ...