Karl's a nice enough guy, but maybe a little lonely. When he discovers a wormhole that allows him to drop into and out of the time continuum, he builds a side business transporting people to seminal rock concerts. See Hendrix at Monterey Pop! Watch the Ramones at CBGB!
When he bumbles a date and accidentally sends a friend to 980, Karl is forced to enlist the help of an astrophysicist to work the science end of getting him back. Lena's a socially awkward genius in punk goddess guise. Of course, there are sparks. Of course, there are complications.
It's a fun, light book full of 1990s music references and the kind of characters to whom you can relate. The time travel begins to make things a little sticky - not everybody is as diligent as Karl about not altering the past - but even at its twistiest the story never gets super sci-fi complicated.
I read it in a single sitting, and it was a welcome departure from more serious topics I'd been pondering. Plus, now I keep trying to decide what my ultimate concert experience would be ...