@Moon: Well it mainly turns around Dracula and the Belmont Vampire Hunter family. Castlevania is actually Dracula's castle, and it reappears every 100 year, meaning a new Belmont, or Vampire Hunter, needs to go face off Dracula to stop him every century, well unless a priest actually revive him before that time.
The game before Symphony of the Night (Dracula X Chronicles on the PSP) is actually Ritcher Belmont's wife who gets kidnapped along with other women, and he goes rescue her in Dracula's castle. He meets, while in the Castle, a youing girl named Maria who's using animal spirits to fight (she's also captive), so he frees her and in the end she helps him recues his wife and the other women and destroy Dracula for the time been...
The game after (Symphony of the Night) is set 5 years after, and is mainly Ritcher suddenly disapearring, while Castlenia suddenly reappear. Therefore Maria (who's now older) goes to rescue him alone, and enters the castle...it then switch to a new character, Alucard (yes, ALUCARD, but this time it's Dracula's half blood son lol), who awaken from his long slumber. He then goes to the castle, you fight, you meet Maria, she fights you, you win, so she agree to let you go help Ritcher, you save Ritcher who had become evil, then you go to the inverted castle (same but really inverted, like you're walking on the ceiling), and then you defeat your own father... And yada yada lol.
Here:
http://en.wikipedia.org/wiki/Castlev...y_of_the_Night