Jesse realizes that the drug dealers who killed Combo are not only selling their blue meth but are using an 11 year-old to do the work, and wants revenge.
He's prepared to kill them and wants Walt to help; he refuses. Jesse demands that they stop using children, which leads to unintended and tragic consequences.
At home, Walt tries to lay down the law as it pertains to his role in the family but Skyler holds her ground and refuses to give him everything he wants.
Jesse confronts the dealers, but as he gets his gun ready, Walt shows up in his car, runs the dealers over, picks up a gun and shoots one.
As the credits roll, he tells Jesse, "run."