The next book of the series!
Father of Nations (A Shelter in Spacetime Book 8):

Sergey has defeated an incredibly dangerous enemy and earned so many rewards, if he was a hamster, his cheeks would explode. On top of that, he’s finally reached Berlin. Unfortunately, it turned out to be a dud, so now he’s heading back to Mother Russia.

How many books will it take him to get there? We’ll see…