Alex is a middle-age professor at a German university who secretly writes popular gay erotica in his free time. While on vacation in Spain, he meets Christian, a barely-legal student who also happens to be German. It's a bit of a meet cute but Alex doesn't want it to be sexual because of the age gap. They stay in contact for years through calls, letters, emails, etc. and even in-person visits but Alex feels his mentee has started to pull away from him. Out of the blue, Christian's lawyer mother calls (it's mentioned they've spoken previously because of the constant contact) to ask Alex about Christian's move to the same university Alex teaches at, which is news to Alex.
Alex has always had an appreciation for Christian beyond just friendship but is really put off by the age gap and also doesn't want him to know about Alex's writing, for whatever reason. As they have more in-person contact, the desire between them grows but Alex's hangups keep getting in the way. He's basically treating Christian like a kid even though he's been an adult throughout the relationship. And Christian has had enough of that.

Horvat is excellent in fitting a ton of story into so few words. Their characters really come to life and you're invested quickly. It's refreshing to have a different setting than the UK or US (which makes sense since the writer is from eastern Europe) and made me really wish I was there in Freiburg. This is also just a cute romantic story about two people figuring out who they are and what they want out of the world and each other.