In an opening voice-over, an evil race of warriors known as The Necromongers, led by the Lord Marshal (Colm Feore) is sweeping across the galaxy destroying entire planets while they search for their promised land, "Underverse". If the inhabitants of a planet will not convert to their fanatical culture, the planet is destroyed using advanced technology. Their only weakness is a race of people called Furions which they wiped out, long ago. Richard B. Riddick (Vin Diesel), is the last surviving Furion in the race.In the next opening scene, a long-haired Riddick is running across the snowy surface of Planet 6 in the U.V. System as a Merc named Toombs (Nick Chinlund) and his crew pursue Riddick in their ship. The Merc flies after Riddick into a cave where Riddick proceeds to kill the crew of the ship saving Toombs for last. Riddick finds out that the bounty for his head is 1.5 million dollars, and was offered by someone on the planet Helion Prime. Riddick throws Toombs off of the ship and flies off to Helion Prime.On Helion Prime, we find the bounty was offered by the same man, Imam, whom Riddick saved from the planet in "Pitch Black" five years ago. Imam (Keith David) has a beautiful wife now and a young daughter. Imam explains to Riddick that he had Jack/Jackie (the gender confused girl from Pitch Black) in his care and then she ran away looking for Riddick. She killed some people and is now residing in a prison on the planet Crematoria. A ghost-like person Aereon (Judi Dench) shows up at Imam's house and explains to Riddick what the Necromongers can do and that they need his help.Just then we see that Helion Prime guards are trying to break down Imam's doors because he has an escaped convict in there. They break through and find Riddick in a dark room with just candles lit. He then says "I hope you're not afraid of the dark" and then snuffs the candles with his hands and kills all the guards thanks to his night vision, which give him the ability to see in the dark.We then see the Necromonger fleet landing on Helion Prime. The Necromongers storm out of their ships killing everything in sight. They find Imam and his family. Imam leads the guards away from his family and they kill him.In what looks like the town hall, the Necromongers have gathered all of the remaining people in a town hall. In there we meet the four main Necromonger leaders, Lord Marshal (Colm Feore), The Purifier (Linus Roache), Vaako (Karl Urban), and Vaako's wife Dame Vaako (Thandie Newton). The Purifier explains to all the people who don't convert to the Necromonger will be slain. Lord Marshal then tells all those who want to join the Necromonger way to bow down. One townsman speaks out in defiance. The Marshal approaches the man and becomes a ghost like form and takes out the man's soul. The man falls dead to the floor. Everyone bows down... except for Riddick. Vaako approaches Riddick and tells him to bow or die. Riddick points out a huge muscular soldier with two axes and says he'd like to take him on. The soldier, Irgun, who was responsible for killing Imam, approaches Riddick and swings his axes at him. Riddick grabs Imam's knife, still stuck in Irgun's armor, and stabs him with it. Lord Marshal claims that was his best man. Lord Marshal has Dame Vaako take Riddick back to the main ship.Riddick is now on the main ship and he sees all the townspeople being converted, which leaves a noticeable mark on the neck. Lord Marshal tells this machine to run a test on Riddick to see what race he is from. The machine starts screaming that Riddick is a Furion and that they must kill him now. Riddick shoots his way out of the ship attempting to escape. We see a Necromonger battleship chasing Riddick through the streets. The ship is unexpectedly hit by rockets, sending it crashing to the ground. We find out the rockets came from Toomb's new crew of Mercs. They capture Riddick and take them back to Toomb's ship.The Lord Marshal orders Vaako to personally track down Riddick and kill him. Vaako asks why he needs Riddick dead so badly. Marshal explains that in a vision he was told he would be killed by a Furion and Riddick is the only Furion left. Dame Vaako talks to her husband, telling him that if he succeeds in killing the Marshal he would become the new king. Vaako ponders this thought and then leaves in search of Riddick.Riddick wakes up in chains on Toomb's ship. They say they're going to turn Riddick over to a prison planet and collect the money on his head. Riddick suggests they go to a prison on the planet Crematoria (where Jack/Jackie) is being held. We find out that Crematoria is a planet with a hostile surface, one where stepping outside for only a few seconds burns you to ash.The ship lands in a hangar on Crematoria. Toombs and his men take Riddick on a skiff to the underground prison of Crematoria. As they speed through a tunnel, Riddick is able to kill one of Toombs' men, throwing him off the skiff. The Prison Director invites Toombs and his crew to stay overnight there so they can discuss the amount of money he will be paying for Riddick. As they are talking Riddick frees himself from his bonds and begins wandering around the prison looking for Jack/Jackie. He finds her. She tells him that she befriended some Mercs and they took her in as a slave. She killed them and got sent here. She says she no longer goes by Jack/Jackie but now her name is Kyra (Alexa Davalos).Riddick tells her that they are going to escape. We see the Sun's pattern on the surface and how it works. Ever so often there is shade. The sun rises again and scorches the surface, burning everything living to ash. After a long discussion Toombs and his crew don't agree with the Prison Director on how much money there being paid for Riddick. They end up killing each other and die.Riddick releases a bunch of the prisoners and explains they'll have to travel on the surface to get back to Toomb's ship. We find out that they are racing a bunch of Mercs who are traveling underground to get to the same ship. As they hike over the terrain of jagged rocks and valleys, the sun rises again and several of them are trapped and killed. Riddick is barely able to rescue Kyra when she falls behind.On the surface they run to the hangar. When they get there they see a small army of Necromongers, led by Vaako. The hangar doors open and the Mercs engage in gunfire against the Necromongers as Riddick and Kyra watch from the mountains. They turn around and see the sun's rays closing in on them. They run down the mountain and join the battle.Kyra is knocked out by one of the Necromongers and taken prisoner. Riddick is shot by Vaako, and he lies out in the open as the sun's rays begin to burn Riddick. Vaako and the Necromongers leave with Kyra. Riddick is dragged to safety by an unidentified individual. When he wakes up in the hangar, he notices he is not alone, The Purifier is there with him. The Purifier is removing all of his Necromonger armor and explains to Riddick that he is also a Furion. He leaves Riddick all of his armor and walks into the sun's rays, falling to ash in seconds.Riddick steals Toomb's ship and flies it back to Helion Prime wearing Necromonger armor. On the Necromonger ship Dame Vaako sees that Riddick is on board because she saw his glowing eyes through the armor. She runs back to Vaako and informs him that Riddick is on board. She tells him to let Riddick almost kill Marshal and then kill Marshal himself so Vaako will become the new lord of the Necromongers.Riddick finds Lord Marshal in the thrown room and tries to stab him from behind but Vaako uses his ghost like abilities to teleport to somewhere else. Marshal then shows Riddick the new and improved Kyra. She has a hole in her neck and has been converted to Necromonger. Necromongers form a circle around Riddick and Marshal as they begin to fight. Every time Riddick swings at Marshal, he teleports somewhere else.Marshal tackles Riddick to the ground and tries to remove his soul. Kyra runs in and stabs Marshal in the back. Marshal hits Kyra, throwing her backwards where she's impaled and dies. Vaako steps in with a huge axe. Marshal asks Vaako to finish Riddick off for him but Vaako moves towards Marshal. Vaako raises the axe to Marshal's head and Marshal's ghost form teleports over to Riddick as Vaako brings the axe down and misses. Riddick takes a knife and stabs it down into Marshal's head and breaks off the handle. Riddick falls back into Lord Marshal's throne. Aereon approaches Riddick and tells him "You keep what you kill". We pan out as we see all the Necromongers bow down to Riddick, now the new leader of the Necromongers.