Carter lands in an awkward situation after S. A. R. A. H. And Andy's nuptials hit a snag; Zane keeps harassing Jo for details; an unscheduled launch presents trouble for the gang.
When Eurekans start behaving oddly, Carter scours the town for a cause - never suspecting that Allison, miles from home, is the one facing real danger.
Carter and Jo try out Zane's new high-powered risk assessment system, but find that even it may not be a match for the dangerous level of competition among Eureka's scientists.
When the microbots assembling the Titan space craft finish their task they opt to take on a new project and proceed to devour Eureka in the process. In isolation for a mission evaluation the Titan team can't tell if the microbot catastrophe is real or just part of the test.
Preparations for the Titan mission have the unintended consequence of turning the local Eureka environment into Titan's. Meanwhile, Eureka couples struggle to come to terms with each other and the DoD sends an investigator to evaluate Jack and Allison's relationship.
As the Astraeus candidates undergo final interviews, Carter and Allison appeal the results of their relationship audit while trying to keep a lid on escalating mishaps around town.
Grace embraces an honor that strains her relationship with Henry while Deputy Andy becomes an accidental guinea pig for the Astraeus mission -- with catastrophic results.
Sheriff Carter and Allison Blake are secretly planning the perfect holiday surprise for their kids, but a mysterious kaleidoscopic wave of color crashes over Eureka, leaving the entire town and its inhabitants animated.