Season 5 of Breaking Bad opened a few months back with a look one year into the future. We see Walter White, head full of hair (or perhaps a wig?) enjoying a free breakfast meal at Denny's, before going out to a car, and seeing a large rifle in the trunk. Last night's episode showed Future Walt going back to his home (now abandoned), and retrieving a capsule of ricin from its hiding place behind a switch cover.
Lost in the shuffle of the Hank-Walt fight , and then Walt issuing the "tread lightly" threat at the end of the episode, was the beginning of the episode, and the beginning of the season: Who is Walt coming back for?
Clearly, the family is gone from ABQ. House is empty, appears to have been that way fro some time, so it can't be them.
Perhaps it is Jesse? He sure is despondent in the last few episodes, last night showed him driving around the 'hood, tossing stacks of cash wherever they may land. My guess is that he winds up either ODing, or takes his own life before the show ends.
Saul? He is the only one that truly knows "all", that is still alive. Could he be a lose end that Walt is coming to tidy up?
Maybe it's Lydia, the gal from Madrigal. She worked out a Czech pipeline for Walt's meth (which we have learned last night has some quality issues). Maybe she is threatening to expose him, unless he comes out of retirement to "fix" the cook.
Could it be Todd? I'm assuming he is now the master "chef", now that Walt has quit the business. His lack of attention to detail (see quality issues above) has caused the quality of the cyrstal to drop significantly. Walt has always been especially proud of his "brand". Maybe he's coming to take back control of his empire?
Or maybe someone we haven't even considered yet.