Season 3 spoilers.
The kids enter their senior year and prepare for college.
One of the kids meets with the dean of Harbor High.
Kirsten is in rehab as the season opens.
Trey is alive and in a coma.
Julie is frustrated with her inability to get money from Caleb's will.
D.A. Caldwell is back and is involved in the investigation into Trey's shooting.
The police still don't have the whole story as to Trey's shooting, it seems the kids aren't talking.
Julie hires a hot shot attorney to help defend Marissa.
Kirsten befriends a woman in rehab named Charlotte Morgan (actress Jeri Ryan)
Charlotte is not all she appears to be.
Sandy, Seth and Ryan try to manage without Kirsten.
Upset by all the attention, Marissa switches schools.
Tate Donovan (Jimmy) may or may not be back for good in Season 3
Someone will leave and some will return according to writer Josh Schwartz
Source:
http://www.soapoperafan.com/theoc/storyspoil.html
More spoilers
Ryan and Marissa have a meeting with the Dean to talk about their future (or lack of) at Harbor.
Jimmy must make once more the difficult decision to leave or stay with his family.
Eric Mabius (Eyes, The L Word) will join the show as the new Dean of Discipline at Harbor.
Marissa is kicked out of Harbor High and starts school at Newport Union where she meets some very "Ryan, Summer, and Seth" like new friends.
A new character is introduced to rival Summer....her name is Taylor.
Source:
http://www.ocfiles.com/forum/t4671.html