Deputy Jo Lupo has just passed the bi-annual D.O.D. re-certification test run by Dr. Bella Pagani with a perfect score and now it's Sheriff Carter's turn. Grudgingly, Carter enters the isolation chamber, leaving Jo in charge of the office, the town and Zoe. The ensuing 48 hours will severely test his fortitude and ingenuity. There will be a serious test for Jo, too.
While Carter grapples with a series of challenges designed to play on his personal fears, Jo steps into his shoes - and they pinch. After a minor tiff with Zane, she's called to weigh in on a new DNA profiling security system. As mayor, Henry isn't happy about it, especially when Jo votes with Allison against him to put the system on-line. After agreeing to let Dr. Stefano make Jo his first subject for DNA security scanning, the device malfunctions and nearly electrocutes her. When she comes to, they realize that a vital spectrometer is missing. Sabotage! Allison wants to pull Carter out of his recertification test, but Jo, despite the jolt she received, insists she can, and will, find the saboteur.
When Jo asks Henry about the missing piece of equipment, he tells her his intramuscular electrode array is also missing. Leaving Henry to ponder a possible link between the two stolen items, Jo heads for the Smart House to help Zoe with homework. Jo finds that walking a mile in Carter's shoes is proving to be a challenge - especially when Zoe wants to blow off work and go to karaoke night at Cafe Diem. Jo's still feeling the effects of her near-electrocution and forbids it, wanting nothing more than to sleep. An opportunity Zoe uses to sneak out.
But Zoe's night out doesn't last for long. Jo catches her performing at the Cafe. Yet instead of grounding her, Jo joins in the fun, drinking too much as she sings and flirts with Fargo. Everyone begins to wonder: What's gotten into Jo? Zane's interest in the situation is peeked, particularly when he walks in just as Jo plants a kiss on Fargo. She insists that she's fine. But Allison and Henry worry about Jo's state of mind after she begins behaving more erratically. Then a third theft occurs and the DNA scanner identifies Jo as the thief. Only Jo knows that someone is stealing her identity, gene by gene. Trapped in that person's body, Jo has to convince a skeptical Zane of her true identity. Reversing the calamity requires a terrifying gamble - one that may cost Jo her life.
Wormholes start popping up all over, threatening to rip Eureka apart unless Carter can stop them.