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.

Samuel prepares for new additions to his family, while Lydia warns him of the consequences. Claire discovers that her roommate Gretchen may have a hidden agenda. Meanwhile, Peter finds an unexpected way to connect with Emma, who would prefer to stay distant. Elsewhere, a different side of Sylar emerges as he desperately tries to remember the person he used to be.

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.

Claire is determined to get to the bottom of the Sorority Rush attacks on her own, until H.R.G. intervenes only to realize he may be the source of her troubles. Meanwhile, Peter's new ability is a perfect fit for his job and gives him the opportunity to help Emma accept her new life. Elsewhere, Sylar's battle at gaining full control over Matt's body escalates with potentially dangerous implications at stake.

As Claire becomes immersed into the world of the Carnival, she becomes increasingly suspicious of Samuel's motives. Hiro is on a mission to rescue one of his own, but has difficulty communicating his intentions to Ando.

H.R.G. recruits Matt to help him take down Samuel, as they use his long-lost love, Vanessa, to lure him to them, but Samuel has his own plans for Vanessa in the works. Meanwhile, Hiro and Ando go to extreme lengths to save Dr. Suresh. Elsewhere, Peter's introduction of Emma to his mother brings forth visions of a very grim future.

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.

Fueled by his vision of Emma in grave danger, Peter attempts to rescue Sylar from his worst nightmare. At the carnival, Samuel reveals H.R.G.s secret past in order to bring Claire to his side. Meanwhile, Lauren makes a bold move to put a stop to Samuel.

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.