yeah i wanna know too i missed pretty much all the seasons until now haha

i haven't watched last night's episode yet....i'll be seeing it this weekend

BUT

sloan was an evil man who ran a team of agents trying to get these artifacts that would lead him to the writings of the "higher source" which they called "RIMBALDI". it was basically to rule the world. anyway these poor agents thought they were working for the CIA and did what he said, thinking they were the good guys. sydney became the double agent to take him down.

so the whole first season was sydney being double agent, she and her Dad (jack) to take down SD6 (the name of the fake "CIA" team) and all led to the destruction of SD6, and sloan. Sloan somehow escapes and finds some of the missing pieces of RImbaldi. in the writings there was something written about a "girl" that would appear to complete or reveal the prophecy of this Rimbaldi. the characteristics of the girl are that of Sydneys and there's a picture of sydney in that book saying that she weilds the power and will leash her fury into desolation.

season two:

they continue to look for sloan....by now he's like the Bin Laden of alias. this season reveals more on what sydney part is and her link to RImbaldi but you still dont get the full answers. they bring in her SD6 partner, they're computer wiz etc and she and vaughn start off their relationship. Anyway, sloan is heading up this new team called the alliance who are bigger and badder than SD6. so it goes through sloan with each passing time gets closer to the end of the prophecy of Rimbaldi. SLoan finally reaches his end with rimbaldi or close to it adn realizes it something to do with inner peace etc. Sydney finds out her mom was having an affair on her dad with sloan....