There are so many locations, each with signifigant info! Find out about all of them here. This also has supporting information on events that occur, and organizations. This includes AMF, Guardians, Factions and war data. If you need to know what happened and why, read this! 02.04.07
In Story Mode, every character is an NPC, so find out about them all here! As with PSO, plot is also told through your expierences with the characters, and not just shown in exposition and explanation. There are plenty of NPCs in PSU, aside from the main story characters. Not all of them are super important, but there are funny and useful things you can learn from them. This also covers characters you NEVER see, unlike other guides. Of course, the main story characters all have huge plots and detailed descriptions. 02.25.07
This is the whole plot of story mode written out for you to read. Clarify details, learn extra info, and find small commentary in here. This also serves as a time line, with events both before and after so you can get the big picture fast!
Online Story Mode Write Ups
Here are write ups of each of the online story missions. These don't work as a play-guide, but they do summarize all experiences, facts, and plot points that appear. This also has speculation for future events and mystery-solving.
Ambition of the Illuminus Story-
A plot write up for the next game in the series. They didn't call it "PSU 2" but rather just subbed it Ambition of the Illuminus. It didn't have any 'Ethan only' ability and its focus was online gameplay and some technological upgrades to the look.