This issue, a fill-in interrupting the ongoing Ka-Zar story (it’s okay, it was a bad story anyway), introduces Gemini. As you might expect, it’s a “twin” based character.
Police officer Damian Link and his criminal brother Joshua get psychically linked (the link is portrayed, below, as a ghost-like creature) when they are knocked into something sciencey. Notice how their last name is “Link”? Yeah, it’s a very “1960s Stan Lee” kinda story.
Gemini will go on to join the Zodiac gang of criminals, of course.