Fantastic Four (1961) #558 1st cameo of the New Defenders

Who are the New Defenders, and why does their appearance on Earth foretell the eventual extinction of mankind? Who has liberated Doctor Doom from his incarceration awaiting trial, and why? And what's up with Valeria? (Oh, and the Fantastic Four are in it too...)

This book features the cameo of Old Man Logan as the Hooded Man.