For the past year or so Cap has been tricked into thinking that for his entire life he was a secret spy and weapon of Hydra. This was done to Cap by the Red Skull by using the cosmic cube. If you want more on that story then let me know and I can write a summary.
Well Cap believes that he is Hydra and that his mission was to infiltrate SHIELD and conquer the US. In this event, Cap begins his invasion and begins to let people know that he is in fact a agent of Hydra.
His plan is very thorough and this book explains it all. You DO NOT need to have read the Captain America: Steve Rogers in order to understand this book. Just read the first page that explains everything before you go on. With that, I really enjoyed this book and hope it has a better ending then Civil War II since we are not getting another major event for another 18 months.