In the Season 4 finale, Peter joins forces with an unlikely ally to rescue Emma. Elsewhere, Noah and Claire fight for survival while trapped underground with depleting oxygen; Hiro reviews his past choices and takes action to stop a catastrophe.
Noah and Matt come up with a plan to take down Samuel using his long-lost love (Kate Vernon), but Samuel has his own plans for the woman. Meanwhile, Hiro and Ando try to save Dr. Suresh; and Peter introduces Emma to his mom, a meeting that leads to bleak visions of the future.
The Thanksgiving holiday prompts Noah to arrange an unusual gathering, while the Petrellis are caught off guard by a surprise dinner guest. Meanwhile, Hiro is held captive by Samuel as Lydia seeks answers.
Claire investigates the sorority attacks, which may have a link to Noah. Elsewhere, Peter finds his job performance improved after gaining a new ability, which also provides a means to help Emma, and Sylar escalates his assault on Matt.
Hiro has another chance to save Charlie (Jayma Mays) when he travels three years into the past, where he also encounters Samuel. Elsewhere, Noah's history with his partner (Elisabeth Röhm) is uncovered.
Matt takes a big risk in order to be rid of Sylar; Noah asks Tracy to help a boy who's had similar experiences to Tracy; Claire and Gretchen go through hazing, but they've got other problems facing them.
Samuel guides Sylar on his journey of self-discovery; Hiro helps Emma understand the potential impact of her ability; and Peter asks Noah to help him find someone who can heal Hiro. Ernie Hudson guest stars.
Samuel prepares to expand his family, but Lydia worries about the repercussions of his actions. Elsewhere, Gretchen surprises Claire with a hidden agenda; Peter connects with a reluctant Emma; and Sylar tries to remember who he was in the past.
Peter deals with repercussions from his heroic acts and meets a new woman with abilities (Deanne Bray); Claire deals with the unveiling of her secret; Samuel goes to great lengths to retrieve memories of his brother; and Matt battles inner demons as Sylar reappears.
Peter returns to his paramedic job; Hiro fears that he's dying; Samuel, Lydia and Edgar search for others like themselves; Claire's secret is threatened by Gretchen, who saw her fall from a third-story window.