Hank Pym takes the fragments of the shattered power ring of the original Squadron Sinister and gifts them to Jan, who is promptly possessed by spirit of Dr. Spectrum, which lives in that gem.
And it wants revenge on Iron Man.
Dr. Strange’s advice is to exorcise the Spectrum from Jan by reuniting it with the original host. For some reason, this means that all the Squadron members will revive as well, because, we’re told, they have all forgotten who they and are living in the world as normal people.
I don’t remember when they got collective amnesia. But then, their presence on 616 Earth has been confusing from the start.
Anyway, all is well in the end and Jan gets cake.