Rating: WARTY!
I guess I'm not an Asimov fan and this is the last of his I will review. I've tried his work before and never got along with it. This one sounded interesting, if a little dumb, premise-wise: "In the twenty-second century Earth obtains limitless, free energy from a source science little understands: an exchange between Earth and a parallel universe, using a process devised by the aliens. But even free energy has a price. The transference process itself will eventually lead to the destruction of the Earth's Sun-and of Earth itself."
The thing is that we already get free energy from the sun without any destruction of anything - if we were only smart enough to understand that and avail ourselves of it. Asimov offers no rationale for a need to try alternate energy sources. That wasn't the biggest problem here though, and I was willing to overlook his gross error for a good story, but that's not what he offered. The story starts with chapter six for no reason I could discern. At first I thought I'd missed something but no - he even has a footnote on that same page explaining that it will make sense, but it didn't!
Instead of counting down from there or whatever, he starts counting up from chapter one and then reverting back to 'chapter 6 continued' periodically. Even that I could have coped with, but the story was nonsensical and utterly boring and I gave up on it in short order. Maybe there's a good story in there somewhere, but I lost patience with it and couldn't be bothered trying to search for one when other books were calling and willing to share their story without requiring a contortionist reading position. I can't commend this one and I'm done with Asimov.