As we've seen throughout Jonathan Hickman's run on both Fantastic Four and FF, there's a longstanding beef between Black Bolt, King of the Inhumans, and the Kree Supreme Intelligence. Both of them have been brought back to life recently, and the latter seems to believe that the former is always destined to destroy him.
Now, Black Bolt has brought the Inhuman city of Attilan back to Earth, because the Franklin Richards of the future told him he had to. If one recalls, Attilan initially left Earth because humans kept getting nosy and trying to hunt down their hidden location to give them static. How will this return play out? How will the enmity with the Supreme Intelligence be resolved? And how in the world did the arranged marriage between Ronan the Accuser and Crystal actuall turn into legitimate love?
Check out this Nick Dragotta preview art from FF #21, featuring a cover by Mike Choi.