In the climactic season finale, everyone bands together in an effort 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.

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.

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.

Hiro's life hangs in the balance as his brain tumor worsens, prompting him to subconsciously deal with some of his past decisions. Meanwhile, Sylar pays Claire an unexpected visit to get answers as to why he isn't quite himself. Elsewhere, Samuel's plan to impress his long-lost love, Vanessa, takes a terrifying turn.

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.

Sylar returns to the Carnival in search of answers and Peter continues to struggle with the loss of his brother. Elsewhere, H.R.G. sets his plan in motion to take down the carnival.

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. Samuel has his sight set on Emma and her ability to complete his master plan.

Is greeted by some unexpected visitors and Samuel's grand plan begins to come to fruition. Meanwhile, Peter struggles to accept the truth and takes extreme measures to get what he wants. Elsewhere, Claire's journey leads her to an unexpected destination.

Noah hosts an untraditional Thanksgiving dinner. Elsewhere, the Petrelli family gets a surprise guest at their table. Meanwhile, Samuel continues to hold Hiro hostage, as Lydia goes in search for the truth.

Samuel learns just how powerful he can become and takes dangerous measures to reach his full potential. Meanwhile, as Tracy begins to lose control of her ability, one of her own comes in harms way. Elsewhere, Sylar continues his battle with Matt.

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.

When Hiro travels three years into the past, he has a second chance to save Charlie from the hands of Sylar. However, Samuel's presence serves to complicate Hiro's mission even further. Elsewhere, H.R.G.'s past with his Primatech partner is revealed.

Matt goes to extreme measures to extinguish Sylar, who continues to torment him. Elsewhere, H.R.G. 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.

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.

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.

As Hiro's life continues to hang in the balance, he distracts himself with saving the lives of others. Meanwhile, Angela tries to help the new Nathan remember his past, at the risk of his remembering too much. Elsewhere, Tracy is determined to get her old job back, but soon realizes that she needs to make more of an impact.

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.

Peter uses his abilities for good, but he is soon called upon to aid an old friend. While the heroes adjust to their new surroundings, a mysterious carnival clan, led by ringleader Samuel sets their sights on familiar faces.

Claire struggles with adjusting to her new life in college when a mysterious death thrusts her into the spotlight once again. Elsewhere, Hiro and Ando continue their noble quest to help people by promoting their abilities. Angela fears Nathan will soon discover his true identity; while Matt is haunted by an unexpected visitor seeking something he has lost. Tracy Strauss and H.R.G. join forces, looking for the key to unlock the motive behind a horrific crime.