As the first half of a two-hour season finale event, it also sets the stage for the following episode ("A Make Kāua"):

Danny is left reeling with anger and grief over the three years he missed with his son, while Steve McGarrett reminds him that saving Charlie’s life must now be the priority. Subplots and Finale Setup

The episode is most famous for its major character development for Danny "Danno" Williams:

It is eventually revealed that Pelham was being tracked because he murdered the daughter of Malcolm Leddy , a man who plans to torture Pelham as revenge rather than see him return to prison. The "Explosive" Secret