A few months before the Battle of Yavin, Rianna Saren, a Twi'lek, started her life of freedom as a mercenary. Rianna had an arrogant streak due to her painful past as a slave. Rianna lost a lekku after Zarien Kheev, the Zabrak slaver who owned her, got angry at her for trying to escape and had her lekku cut off. Rianna eventually had a prosthetic replacement fitted. Rianna started off her mercenary career on Coruscant, but she often had to flee from Imperial scout groups.
Rianna fighting stormtroopers on Tatooine.
Saren eventually was contacted by Kyle Katarn, who asked her to steal an Imperial shipment of Mirkanite from a Black Sun warehouse. She decided to do it, for a price. She infiltrated the innermost area of the warehouse, killed many Black Sun guards, but was captured and accidentally activated Zeeo. Zeeo freed her from her cell and they attained possession of the Imperial shipment and brought it to the Rebellion. Leia Organa was very grateful and asked Rianna if she would go to Alderaan. Rianna agreed and successfully shut down an Imperial drug chain. On Alderaan she confronted and killed Slak Sagar, then took his heavy blaster. While on Alderaan she learned from Princess Leia that shipments of the drug were on Mustafar where it was being used to increase the slave production of Mirkanite. Rianna set out to stop production at the factory.
Rianna and Zeeo look upon the Death Star I.
She infiltrated the factory and found some Wookiee slaves. The leader of the group said where the drill was in the factory. She deactivated the drill shaft and set off explosives to destroy the entire facility. She then came across Kheev and followed him to Tatooine, where her ship was shot down by Boba Fett in the Slave I. While on Tatooine she located and killed the Twi'lek slaver Sedriss after finding out where Kheev was located and then took his Blaster Rifle. He was in another part of the town and when she found him in an arena he let a rancor loose. Rianna Saren and Zeeo killed the rancor. Kheev then captured her and took her to Despayre, where she found out about the Death Star.
Rianna escaped the prison on Despayre and managed to make her way onto the Death Star before Despayre's destruction. Upon arrival on the Death Star she headed to the Communication center and told the Rebels about the battlestation. She then stole an Imperial ship and headed to Danuta, where the plans of the Death Star were being held by Kheev. Rianna fought her way to Kheev and killed him in his personal battle armor, though not before Kheev was able to take a pot shot at Rianna. Zeeo sacrificially took the shot and was seriously damaged. Rianna took the Death Star plans from Kheev's body.
Rianna holding Zeeo, walked to her transport ready to continue her mercenary work.
Rianna fighting a rancor.
Throughout the game, players are confronted by enemies, whom they must fight cooperatively, controlling both Rianna and her droid Zeeo to accomplish their missions. Players are able to set up holographic disguises to fool Imperial Royal Guards, and command gun turrets. Rianna as the main character is not a Jedi, so there are no Force powers or lightsabers. A multiplayer mode allows players to combat each other using droids from the same class as Zeeo.
There are significant changes between DS and PSP versions: the DS version allows the player to use a unique "Dual Cannon" attack by holding the X button while at "Maximum Alliance" (boosted by using Zeeo in Combat), while the PSP version has holographic disguises.
There are some inaccuracies contradicting the 1995 PC game Star Wars: Dark Forces where the Death Star plans are stolen by Kyle Katarn on Danuta. However, it is stated in the game that the plans that appear there are the updated plans that the architects on Danuta requested. Another error is also regarding Katarn, where in Dark Forces he is a shaved young man, and in Lethal Alliance is bearded and older, as seen in New Republic era publications (Star Wars: Jedi Knight: Dark Forces II and later).