Sheriff Jack Carter is caught in a time loop and must find a way out.
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In Carter's own personal "Ground Hog Day," he relives Allison's wedding to Stark over and over again, only he can't get anyone to believe him. Plus, Allison asked him to walk her down the aisle, compounding his misery.
Carter's New Age sister shows up for a visit, cats in tow, and proceeds to totally spoil Zoe, undermining Carter's authority.
Each 'resetting' of the day is preceded by a blinding flash while at the wedding ceremony, just as Henry (who is officiating) asks if there is anyone who can show cause etc. etc. etc.
It turns out that Stark's plan to have Eureka set the time standard (instead of Greenwich) by way of some kind of super atomic clock (and the anger of Leo, the Time Maintenance guy who got laid off) is what is causing the time loop. But can Carter fix it before everyone is redacted from the universe? And at what sacrifice?