A Global Dynamics researcher has a breakthrough on her project visualizing another dimension. And since GD's experiments have a bad tendency to affect the entire town, Sheriff Jack Carter heads over to check it out. What he sees blows him away. The project has revealed a parallel universe, complete with another Eureka-one in which Carter doesn't exist! But as the two worlds begin to bleed into each other and residents confront their alternate selves, Carter may be the one man who can keep both Eurekas from being destroyed.

Even the brightest of Eureka's residents can't read someone else's mind. Then Global Dynamics develops the Brain Box: a device capable of capturing and storing human thoughts. When the Box starts messing with people's minds, Sheriff Jack Carter will have to keep his thoughts to himself if he's going to save the town from going out of their heads.