Do yourself a favor. If you have not been following this series, do not try and pick up on it mid way through the season.
Sci-Fi runs marathons and will show all the episodes of Heroes again between the end of this season and the start of next season. They do that with several series.
Also, Heroes shows on NBC (SciFi's parent company), but do not expect to see the marathon events.
This series is a bit like "Lost" in its formula. Where there are many story threads through the main story arc. Unlike 'Lost', 'Heroes' actually does end its threads and ties things up pretty quickly. But, there are things going on, which you do not know about until they happen. Kind of a cool touch there. Who would have expected the cheerleaders real Dad to be who he is?
The one thing I am wondering about is; This arc started with a specific ending in mind. Once that ending happens, will the series end? It would seem to be a difficult premise to maintain after then end of this season, unless they bring in a whole new set of heroes.