Vin Diesel returns as the nocturnally gifted antihero Riddick in this sequel to the 2000 cult item Pitch Black. Riddick, on the run from the law and evading mercenaries eager to claim the price on his head, seeks refuge on the planet of Helion, only to discover he's walked into a world in chaos. Helion has been seized by the Lord Marshall (Colm Feore), leader of the Necromongers, a race of bloodthirsty warriors determined to wipe out humanity throughout the universe. Aereon (Judi Dench), leader of Helion's "elementals," pleads with Riddick to join them in their fight for survival; Riddick agrees, hoping to fill out some of the blank chapters in his history along the way. As he plots his battle strategy against the Necromongers, Riddick becomes reacquainted with Kyra (Alexa Davalos), whom he knew as a girl but has since grown into a strong and beautiful woman eager to join him in the fight against the Lord Marshall.
by Mark Deming synopsis