Spoilers ahead Episode 20 of The Flash Season 4, called "Therefore She Is."
The Thinker has emerged as one of the most formidable foes in the Arrow-verse to date, and The Flash hasn't given Team Flash too many breaks as he works to put his "Enlightenment" into action with the help of Marlize. The Flash has teased The Enlightenment for a while, but we didn't know any more about it than we did about Mystery Girl... until the events of "Therefore She Is." The episode revealed The Thinker's plan with The Enlightenment, and it proves that The Thinker is even crazier than we thought.
As it turns out, The Enlightenment is the name given to The Thinker's plot to "reboot" human brains, breaking them down into simplified states via the use of dark matter. Technology was ruining humankind, according to The Thinker, and humankind needed to give up on technology and revert to a simpler state of being.
All throughout Season 4, The Thinker has been putting the pieces together to start The Enlightenment. In "Therefore She Is," he used all the powers he accumulated from the bus metas to rob a variety of valuable materials from companies with Marlize at his side. Marlize was more reluctant than The Thinker to use lethal force on people who got in their way, although she still seemed to be on board with his plan in general. Team Flash eventually realized that the stolen items were being used to create a number of satellites that had the capacity to bathe the planet in so much dark matter that all human brains would be rebooted and simplified. Technology would no longer be a problem, and The Thinker would be able to rule over everybody.
Well, if any viewers had any doubts that The Thinker was a total madman prior to this episode, the details of The Enlightenment probably took care of those doubts. The Thinker and Marlize triumphed over Team Flash and successfully stole all the equipment they needed for their plan, although Marlize wasn't happy when she heard him talking about wanting to control. The man she fell in love with wanted to fix humanity, not control humanity. She declared that her husband was The Thinker's first victim.
Unfortunately, this declaration didn't lead to a total change of heart for Marlize. She didn't suddenly switch allegiances to Team Flash. No, Marlize now wants to complete Clifford's original goal before he became The Thinker. Although originally appalled at his beliefs regarding too many people existing on Earth and the crippling nature of technology, she came around after an incident when she was volunteering with the Peace Corps in Kenya. Just after she perfected a water filtration device that could save the lives of many local women and children in need, a militia attacked and slaughtered the innocents to take the device for themselves. It was enough for Marlize to decide Clifford had a point and The Enlightenment needed to happen.
The good news is that Marlize trapped her husband in his pocket dimension, cutting him and his pilfered powers off from Team Flash and other innocents. The bad news is that Marlize is brilliant, motivated, and in possession of The Thinker's chair. Team Flash also witnessed her talking The Thinker out of killing Gypsy, which could lead them to erroneously believe that she would be their ally. Marlize has an edge on just about everybody. Could she turn out to be the real big bad of The Flash Season 4?
We'll have to wait and see. The episode also confirmed a key detail about Mystery Girl, and there's a lot to think about while we wait. New episodes of The Flash air on Tuesdays at 8 p.m. ET on The CW. For more important superhero info, swing by our rundown of superhero TV dates. For some non-superhero viewing fare, take a peek at our summer TV premiere schedule.