Such about a powerful episode, and the ending gave me the creeps.
Just like Vince Gilligan said in an interview, Mike is a "Samurai without a master". He's an Honorable man, who tried to stick by his own rules. He tried to stick by the rules as a cop, and then an innocent woman was killed. I bet that incident made him quit, and become a PI. Then, along comes Gus Fring, who needs someone who is willing to "flex the rules" a bit, but won't go too far. And Mike said yes, because he needed money for his grandaughter.
I'm pretty sure the only reason Mike went back to working for Walt is out of fear that he might kill her.
Walt is just awful in his manipulations of the people around him. And it's going to bite him in the ass.