Dealers who are selling the meth that Walt and Jesse are cooking and using kids to sell it. So Jesse concocts a plan to kill them then tries to get Walter to go along with it. Already struggling with the choices he's made and who he has become, Walter refuses. But when he realizes that Jesse is going ahead with the plan anyway, he arrives just in time. If "just in time" means in enough time to run the dealers over with his car then shoot them in the head.
Jesse wants revenge when his friend is killed by a couple of dealers.