Fantastic Four #105-116 tell a long story featuring another Thing cure gone wrong, a villain named Janus, and a villain called Overmind. It’s an arc that runs through several artists.
It starts off with a great street scene. Crystal is feeling sick and Ben is being teased by a kid.
Reed figures out that it’s pollution and she can’t survive in the world of humankind.
Then, Reed tries to cure Thing but in the middle of the process there’s a threat on the streets of New York, and so Reed has to “freeze” Ben midway. The cliffhanger has Reed getting ready for the final step.