According to the official movie site:
Riddick has spent the next 5 years on the move among the forgotten worlds on the outskirts of the galaxy, eluding the mercenaries bent on collecting the price on his head. Now , the fugitive finds himselfon planet helion home to a progressive multicuntural society that has been invaded by lord Marshal a despot who targets humans for subjugation wiith his army of warriors known as necromongers.
Exiled to a subterrean prison where extremes of temperature range from artic nights to volcanic days, Riddick encounters Kyra, the lone survivor from an earlier chapter in his life. His efforts to free himself an kyra lead him to the necromonger command ship, wher he is pitted against the lord marshall in an apocalyptic battle with possibly the fate of all beings-both living and dead-hanging in the balance
