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.

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.