Karl Bender used to play in a moderately famous band in the '90s, but now he's a middle aged bar owner who doesn't really know what to do with his life. That is, until he discovers a wormhole in his closet. Karl and his best friend Wayne start a side hustle charging people for trips to the past to see their favorite bands, until Karl accidentally sends Wayne back to 980 instead of 1980. So he seeks help from an astrophysicist named Lena, and while working to bring Wayne back, the two fall in love with each other while also wrestling with being able to visit (and possibly change) the darkest moments of their pasts. 

Wow, this book! It's funny and nostalgic about music in exactly the way I like to be. It also engages seriously with not only the logistics and potential disruptive effects of time travel but also possible emotional effects on the traveler. Karl, Lena, and other minor characters all discuss an unexpected deep sadness upon returning and knowing that you're back in your regular old life. This, then, is how Karl and Lena both end up compulsively visiting the worst moments of their lives and wrestling with whether or not they should attempt to change the course of their own lives. 

I will note that the traveling system is definitely a "reverse the polarity" sort of situation - nothing is really explained and we just go with it - but EVERY ANXIOUS WAVE has tremendous heart for a book that, on the surface, seems like just a funny thought experiment.