Duvall briefly helps Shane in his few missions. He guides him through his first mission by telling him how to use his Nectar administrator. They then unite, and prepare to clear out the Promise Hand rebels that have surrounded a crashed cargo plane carrying Nectar. Once the area is cleared, a Mantel drop-ship picks them up and returns them to the Mantel Land-Carrier.
In the second mission, while on the drop-ship, Duvall lectures Shane about how emotions he feels, like: love, joy, hate, etc... are just a mixture of chemicals interfering with his brain. When the drop-ship pilot spots Gabriel Merino Duvall orders Shane to pursue Merino in a Boxcart, while Duvall and his team pursue him from the air.
When Shane reaches the smelting plant, He finds Merino in a small room and keeps him under guard until Duvall can arrive. Shane then gets lectured by Merino. Not soon after, Duvall bursts in, knocks Merino unconcious and drags him into the nearby elevator. when Merino regains conciousness Duvall tells him that he is allowed to take away one of Merino's fingers as payback for stealing Mantel's Nectar. He pulls out his knife and cuts off Merino's index finger as he screams in pain. Shane gets uncomfortable with the situation. As they leave the elevator, a drop-ship awaits them. They get on board, but Shane is confused over whether he should get on board or stay behind, due to his discomfort. Duvall then calls Shane an ape; which in Duvall's perspective is someone who allows the chemicals in one's brain to control them. Shane then gets aboard. Peshy then suggests that Merino took more than one finger's worth and suggests that he should cut off Merino's hand instead. Duvall agrees and pulls out his knife, ready to cut off Merino's hand, as Shane pulls out and aims his pistol at Duvall. Duvall says "Typical, what are you gonna do? Huh? Shoot me?!" As he is about to cut off Merino's hand, Merino kicks Duvall and battles with him. Peshy tries to shoot Merino, but in a split second, Duvall punches Merino and Peshy misses... Shooting the pilot and causing the drop-ship to crash.
They are all taken into safety by the rebels. As Shane awakes and walks over to the local hospital with Merino, a woman can be heard screaming as she is pushed out of a window by Peshy. Duvall then bursts out of the hospital doors and confronts Shane and is about to shoot him when a squadron of Rebels attack, causing him to fall back. He then jumps in a truck and speeds off... leaving his other team mates behind.
In the last mission, Duvall and Shane meets face to face once again. Duvall is worn out and useless without his Nectar. This is an advantage to the player to kill him faster. When he dies, he squirms on the floor bleeding and cries in pain and agony as Shane drops to knees in sadness. Duvall whimpers his last words to Shane: "Shane... Please... Don't tell my mom..." Shane then softly replies by saying "Okay..."
Duvall is a sub-boss in one of the rebel missions. He can be seen in the drop-ship. The player's job is to damage the drop-ship enough that it will pull out before it shoots down the rebel helicopter.
The second time Duvall is encountered an a boss is in the final showdown on the bridge of the Mantel Land Carrier, where his lack of Nectar make him vulnerable, and allows Shane to finish him off.
- In the mission, Caridad Quarry, if the player proceeds downstairs without pulling the second lever, Duvall will insult them by calling them a moron.