By the time Gerber wrote this, he probably knew he would be leaving the title soon, so the intricate plots and threads he’d been working on for the past year-or-more needed to be wrapped up quickly. And as a result, it’s a little rushed.
The first Defenders annual wraps up the Nebulon/Headmen stories, as these two different villains are trying to take over the world and the team tries to stop each of them.
Jack Norris goes undercover to infiltrate the Headmen and tells them that there are four separate attempts in four different locations to manipulate the world’s political order and make Earth vulnerable to the Headmen. So, the team pairs off and goes to these locales to fight individual Headmen. It’s a pretty standard approach for an annual-break up the big team into manageable groups and have them do stuff on their own.
Both Power Man and Red Guardian are still with the group.
Nebulon is attempting to control President Ford, who makes an appearance on the astral plane with Dr. Strange.
In the end, Nebulon just leaves because it’s too much trouble to help humans. Can’t say I disagree.
This is part of the “Headmen” saga, which is the third-best Steve Gerber story ever.