Here's the official synopsis, which has changed a few of the details you know from the comics:
After a violent shipwreck, billionaire playboy Oliver Queen was missing and presumed dead for five years before being discovered alive on a remote island in the Pacific. When he returns home to Starling City, his devoted mother Moira, much-beloved sister Thea, and best friend Tommy welcome him home, but they sense Oliver has been changed by his ordeal on the island. While Oliver hides the truth about the man he's become, he desperately wants to make amends for the actions he took as the boy he was. Most particularly, he seeks reconciliation with his former girlfriend, Laurel Lance. As Oliver reconnects with those closest to him, he secretly creates the persona of Arrow - a vigilante - to right the wrongs of his family, fight the ills of society, and restore Starling City to its former glory.
Arrow also stars Katie Cassidy as Laurel Lance/Black Canary, Colin Donnell as Tommy Merlyn, Willa Holland as Thea Queen, and Susanna Thompson as Moira Queen.
The pilot episode was directed by David Nutter, whose other TV work includes episodes of Game of Thrones.