Spoilers

[serojay]

Charlie will return in season 4.
I'm assuming this is related to Hiro's time traveling to moments in his past.

[Isaac Mendez]

It will be in episode 8, "Once Upon a Time in Texas."

[Grim Reapster]

Peter Petrelli (Milo Ventimiglia) returns to work as an ordinary New York City EMT, but he uses his abilities to save lives. Peter has become obsessed, looking for redemption and shutting out the rest of the world he once knew. How can he forget the past and begin anew? Peter’s life will quickly change when a hearing impaired woman, Emma (guest star Deanne Bray), enters his life. Emma has used her disability as an excuse to shut herself off from the world. But as a new and unique ability manifests, the shell she’s built around herself will begin to crack apart – as will Peter’s.

I'm thinking that this new woman is just what Peter needs in order to return him to full power. I've had this suspicion that there's nothing different about his ability. His power is empathy. It works by him opening himself to the emotions of others. Which originally came naturally to him.

But Peter's recent dealings with his own family have left him closed off emotionally. Once this woman cracks through his "Shell", I suspect that he'll start absorbing powers again....

[Isaac Mendez]

Emma is neat. I hope that he and her do get together. It would make me like Peter again.