One key event could be Naruto's discovery of Orochimaru's plan to harm Hiruzen. This might prompt him to take immediate action.
In the fanfiction, the key events might start with Naruto sensing something wrong in the village. He then starts to investigate and finds out that Orochimaru is after Hiruzen. Naruto begins to gather his strength and allies. There could be a battle sequence where Naruto battles Orochimaru's minions on his way to Hiruzen. Once he reaches Hiruzen, he has to overcome Orochimaru's final defenses and then safely extract Hiruzen from the dangerous situation.
Another important event would be Naruto's face - off with Orochimaru. During this, Naruto shows his growth as a shinobi by using his skills effectively. He might also have some emotional moments where he remembers his training and the people who have supported him, which gives him the strength to keep fighting. And finally, the moment when Naruto actually saves Hiruzen, which could be filled with a lot of tension and relief.