So my WIP is divided into three parts, each with its own POV character and main characters and its own conflicts. There is some small overlap between the parts, since they're chronologically sequential and separated by about a generation. The three parts together have an overarching theme.

My question is, how might one retain a reader's attention between three basically different stories? Is it possible to get them to identify with three very different characters who are in three very different situations? Are there any tricks for providing a sense of continuity, or will readers just feel betrayed when I drop one POV character's viewpoint for another POV character in the next part?

Nevertheless. I will not let that stop me from having opinions.

The shifts in Liebowitz were pretty big, though, and it did take some effort to make the jump and re-engage in the story.

Perhaps if you make smaller jumps, it will be less jarring? You mention overlap between the generations. If you prepare for the leap it may help. For example, maybe if, say, towards the end of Part One you devote a reasonable amount of space to Character X, the reader will not be as jarred when, in Part Two, you shift to Character X's POV, as they might be if Character X is a totally new character that they have to get to know.

I would also make a point of a) leaving Part One on a cliffhanger, and b) opening Part Two with a killer hook. I mean you'd want to do that anyway, but I'd go out of my way and obsessively work at it. Use every trick at your disposal to carry the reader over the jumps.

You can also try to let the reader know *in advance* that there will be POV shifts. Things like a table of contents, and a page that says "Part One: Derek the Evil Robot Monkey Killer" followed by "Part Two: Clarissa the Evil Robot Monkey Savior" can set things up.

in GW, there was a common theme and premise that carried things through.