Claire, back home in California, begins attending college, but is having difficulty adjusting when a mysterious death of a student during the orientation puts her back in the spotlight. In Japan, Hiro and Ando continue their quest to help people with abilities and go so much as to advertise themselves. Meanwhile, Angela fears Nathan/Syler will discover his true identity. Matt tries to settle down back in Los Angeles and raise his son and not worry about unexpected visitors. Elsewhere, Peter is using his ability for good when a mysterious carnival clan, led by Samuel Sullivan, arrives in town which could spell trouble for him and everyone else.

Claire and her new friend Gretchen investigate the death of Claire's roommate Annie, while Noah comes to Peter for assistance. Samuel and Edgar recover the compass, Hiro realizes his new destiny, and Matt is tormented with mental images from a dangerous foe.

Peter faces unexpected consequences for his heroic acts and encounters a reluctant new hero. As Claire continues to adjust to college life, she must figure out how to deal with her ability having been revealed. Meanwhile, Samuel moves heaven and earth to recapture the memories of his late brother Joseph. Elsewhere, Matt struggles with his internal demons as Sylar mysteriously resurfaces.

Under Samuel’s guidance, Sylar starts on a path to rediscover his true identity. Hiro helps Emma accept and understand the great possibilities that go along with having an ability. Meanwhile, Peter enlists HRG to help him find a healer who can save Hiro’s life.

Matt goes to extreme measures to extinguish Sylar , who continues to torment him. Elsewhere, HRG calls in a favor from Tracy to save a troubled young boy whose misfortunes resemble her own. While Claire and Gretchen are being hazed by their new sorority sisters, they realize pledging might not be their biggest problem.

H.R.G. enacts his plan to take down the Carnival with the help of Lauren and Suresh. Sylar visits Matt looking to understand his desire to make a human connection, but Matt has a plan of his own. Meanwhile, Peter warns Emma of Samuel's intentions after his grim vision of the future.

Everyone bands together to try to stop Samuel from taking the lives of thousands. Peter joins forces with his most unexpected ally to save Emma. Meanwhile, H.R.G.'s life hangs in the balance as he and Claire find themselves trapped underground with oxygen quickly running out. Elsewhere, Hiro starts to come to grips with the decisions he has made and is called into action to help stop a disaster.