Hiro and Ando successfully broke Mohinder out of the mental hospital. You know, because we've been SO concerned over his fate for the last few weeks. Ando then used his powers to short-circuit Hiro back into normalcy and the trio transported away from danger - and into Noah's living room.
Samuel tracked down his long-lost love, Vanessa. He basically kidnapped her and brought her to the carnival, promising to show her something truly "beautiful" by the end of the episode.
Parkman made an appearance, trying to help HRG locate Vanessa and, eventually, Samuel. This plan went awry, however, and Parkman was left back at home, cooking dinner for his wife and son and feeling useless, like his fear was letting all his friends down.
Peter took his mom's dreaming power so he could see into the future and understand why she so feared Emma. In his fantasy, he saw Emma killing thousands of people, somehow due to the use of her cello. As a result, he went over there and destroyed it, very much to Emma's chagrin.
Finally, we never saw Sylar, but we did see Claire acting a bit strangely when HRG went to visit her at college. It stands to reason that Sylar may have been in her room or playing some role in that scene. Still, it was a terrible decision by the series to not show him or follow up on this storyline at all, just a week after its cliffhanging conclusion to an episode that featured him.
Source: TV Fanatic