Plastic Man 6 (Sept/Oct 67) is the only issue from this run to contain two stories, instead of one full-length one, both of which are by Drake and Mortimer.
The first of the two stories is also the final tale in which Dr. Dome appears.
As the story begins, Dr. Dome sets out to rob a bank, but gets stopped by a new villain on the scene, the Sphinx. Dr. Dome is worried that the Sphinx will succeed in killing Plastic Man, which he considers his goal in life.
So the next time Dr. Dome goes into action, trying to rob a baseball stadium during a game, and both the Sphinx and Plastic Man show up, Dr. Dome makes a deal with Plas to work together to defeat the Sphinx.
As it turns out, Dr. Dome really doesn't do much to help. And Plas doesn't even have to try very hard to beat the guy.
At the end the two old foes part as enemies once more. Dr. Dome once again tries to kill Plastic Man, and the hero once again turns the tables on him. Since we never see Dr. Dome again, I like to think the bomb actually just killed him.
The second story, featured on the cover, gives more attention to Mike DeLute and her scheming mother.
While Plas and Mike are at a disco, Goldzinger shows up, with his gold-attracting magnet he uses for crime. Plastic Man tries to stop him, but Goldzinger reverses the polarity, making all the gold attracted to Plas. This causes the crowd to swarm the hero, and Goldzinger gets away.
Later, we see Goldzinger working with Mike DeLute's mother, both plotting together against Plastic Man. Goldzinger takes the opportunity to rob the DeLute mansion, though, and tries to skip the country. This leads the mother to work with Plas to get her gold back. So in both of this issue's tales Plastic Man works with his constant foes.