"Like a Phoenix!"
Continued from Avengers (1963) #263.
The Fantastic Four return from space to find the Avengers have discovered a pod-like object of unknown origin in Jamaica Bay. Upon further analysis, it is revealed that the pod houses Jean Grey of the X-Men. When the pod finally releases Jean, both teams assist her in trying to figure out what happened and how she wound up in her cocoon-like state. What they learn is she was put there by the entity known as Phoenix, who took her place while she healed from life threatening injuries. This story continues in X-Factor (1986) #1.