In the climactic season finale, everyone bands together in an effort to stop Samuel (Robert Knepper) from taking the lives of thousands. Peter (Milo Ventimiglia) joins forces with his most unexpected ally to save Emma (guest star Deanne Bray). Meanwhile, H.R.G.'s (Jack Coleman) life hangs in the balance as he and Claire (Hayden Panettiere) find themselves trapped underground with oxygen quickly running out.
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