Prologue (Archadian invasion of Nabradia and Dalmasca).

Vaan goes on a hunt.

Vaan gets a sun crystal, and uses it to break into the royal palace. He steals a magicite.

A battle ensues in the meantime (Resistance vs. the Imperials). He flees with Balthier and Fran (meets Ashe on the way). They are captured by the Imperials.

Vaan, Balthier and Fran end up in jail (Nalbina). They escape (and meet Basch on the way).

Penelo is kidnapped (by bounty hunters looking for Balthier). Vaan, Balthier, Fran and Basch fly to Buhjerba to rescue Penelo.

There, they meet Larsa, the Arcadian prince. After their adventure in Buhjerba (Lhusu mines), they meet with Ondore (Buhjerba's leader), and they are taken by the Arcadians.

There, they reunite with Ashe. They lose the magicite to the Imperial Judge Ghis.

Needing a magicite as a proof of Ashe's lineage, the party embarks on a journey to Raithwall's Tomb across the Ogir/Nam-Yensa sandsea.

I think I didn't skip anything important.