Overwinter picks up where Frostbite left off, with Chey and Powell travelling north, away from Port Radium. Powell still insists that there's a cure for lycanthropy and he's determined to find it. Along the way, Dzo turns up again, as does a new character, Lucie, with whom Powell has a past. Lucie wants Powell for herself, and to make matters worse, she's on the run from Varkanin, a Russian who she's made an enemy of. Unofficially backed by the Canadian government, which is determined to rid the country of werewolves for financial reasons, Varkanin chases the foursome to the Arctic Circle while Powell looks for clues to a cure that no one is sure even exists.
Though Overwinter is similar to Frostbite: Chey and Powell are being hunted and their wolves hatred of humans results in a body count, in the sequel we learn more about Powell and his past, the origins of the curse and about spirits like Dzo. An unforseen problem for one of the characters makes it essential for them to find the cure quickly if they're ever to hope for normal human lives again (or as normal as can be after having been wolves who've killed people). There was plenty of action and I thought that the characters' goal, to rid themselves of their wolves, made this book a more interesting read than the first.
The one thing that I was a little disappointed with was the ending, and by that, I literally mean the last few pages. The conclusion seemed a bit abrupt (and I thought one thing that occurred was a little odd) after all the time spent leading up to it. Additionally, there was no explanation of what happened, or might have happened, after the last scene. If there was to be a third book, then no problem with the ending, it's just a cliffhanger. However, it doesn't seem like the author left much room for another book, in which case some sort of epilogue would've been nice. I realize this is a bit vague, but I don't want to give away what happened in those last few pages. Unlike what another reviewer said, I wasn't really satisfied with the ending, however, I'd still recommend Overwinter, especially if you liked Frostbite.