Tether picks up where Tandem left off--Sasha is back on Earth, having left Aurora and her love, Thomas, behind. She is trying to fit back in but it's almost hopeless--nothing is working out and her mind is preoccupied with what is going on on the other world. Brought to a man who knows something about both her deceased parents and alternate worlds through the clue of a folded paper, Sasha learns she can go back to Aurora, and she does. Once there, however, things become way more complicated; a third analog, Selene, has shown up, and she needs both Sasha and Julianna to accompany her back to her own universe in order to save it. The problem is, Julianna's disappeared again, and Thomas seems to be acting oddly at times, and everything seems to be much more dangerous than it was the last time Sasha was on Aurora. Making it all even more complicated is the "tether"--the invisible link between analogs that ties Sasha, Selene, and Julianna together, even allowing them to communicate through thought. Sasha is desperate to break the tether, but Selene needs it intact to save her world.
This second installment of the Many-Worlds series is another page-turner, with one event after another delaying finding Julianna and many heavy decisions being made. As a bridge novel, it held my interest well and moved the plot along, though I was a bit disappointed to see that we were in for another round of "Where's Waldo" with Julianna. Selene comes off stiff and wooden in contrast to the emotional Sasha, but that's likely done to show the difference in the two identical analogs. The developments are definitely way more complicated than they were in Tandem, and the risks are greater in lots of ways. Sasha is going to have make up her mind about a lot of things, and this novel sets everything up well for a big finish.
One minor issue I have is the continued use of "in Aurora". I know it's nit picky, but if it's an entire world, shouldn't it be "on Aurora" rather than in? Every time I read that phrase, I imagined the characters literally inside the planet. Maybe I've misinterpreted it, but it pulled me out of the story every single time. But beyond that very minor annoyance, I felt that the plot, if fairly predictable, was well-executed and kept me entertained throughout. I'm excited to see where we end up and can easily recommend this novel as a good middle installment in the series.