Send any character to the "B" that now appears on the map at Cape Catfish, on the Eastern Coast. The team will meet with their FIB contacts, Dave Norton and Steve Haines. Due to poor prior communication the two agents are forced to join the infiltration team. Haines assigns Franklin and Trevor to get the getaway. Norton, Haines, and De Santa then don Scuba Gear and get on a dinghy with Michael at the helm.
At the start you control Michael. Follow the yellow dot on the map to the destination, going south along the coastline into the bay just off-shore from the Humane Labs and Research Facility. When you reach the destination , Dave reports that they can reach the lab via the use of an underwater discharge tunnel. The agents drop into the water. Press the indicated button on the screen to join them.
Follow Dave and Steve (appear on the radar as small blue dots) to the discharge tunnel outlet (the yellow dot). Swimming to the destination will trigger a cut scene: Michael approaches the metal grill that covers the tunnel outlet. Using the controls that show up on the screen, slice through the grill using the Oxy-Hydro cutter. Steve points out that it burns at over 3500 degrees and its fuel is limited so use it sparingly; the fuel level is displayed in the lower-right corner. Each burn is not complete until you hear a "clunk" noise and the green spot turns into a glowing red cut line. In order to remove the grill, do this for all 26 spots.
Once the cutting is complete, Michael pulls down the grill. Swim down along the vent, then glide carefully between the blades of the two turbines. At the two-way vent opening, swim through either of them, then continue past the third turbine. When you finally reach the big open room at the end, swim left then upwards where you will find a ladder. Surface from the water and climb it. Once at the top a cut scene will play out; Steve and Daves plan is pretty sketchy and Michael is assigned use of the Stun Gun.
Once control returns, Michael is automatically armed with a stun gun. Dave takes the doorway as Steve decides to lead from the rear. Follow Dave down the hallway and stun everyone he holds at gunpoint. Proceed around the corner to the Floor -3 elevator and stun the scientist who emerges from it. Walk Michael over to the fallen scientists access card (appears as a green dot on the radar) and take it. Afterwards, get in the lift which will trigger a short cutscene.
When the elevator stops at floor -1, follow Dave to the laboratory 1 doorway. Stun the white-coated workers then continue down the hall and around the corner to the Cold Room doors. Join the FIB duo as they wait for the security team to enter. Stun both of the guards that appear and follow the agents down the hall to a room marked Decontamination 1. Approach the security door and Michael automatically uses the previously acquired card to gain access. In the next area you will find a lone worker in a red lit room with a security door that can only be triggered internally. The other scientist enters from the other door, Steve backs him into the red lit door as collateral to intimidate the worker in the room. It works and he opens the door for you. Zap both of the workers.
Now enter the red lit room and approach the counter, which appears on the radar as a small green dot, which triggers a cutscene: Michael carefully extracts the nerve agent tube from its holding container. When control returns, exit the room and follow the agents down to the doorway labeled Analysis.
At this point you need to swap out the stun gun to a more lethal weapon. Security guards appear out of the doorway labeled "Sample Storage Loading Bay". Gun them down and start following the signs toward the loading bay. Be sure to keep checking your radar for any more red dots that appear on the map that indicated enemies as more guards lurk up ahead, including one around each corner. Use Michael's special ability to clear the corridor. Keep following the signs leading to the storage loading bay.
As you get closer to the bay, you hear monkeys chattering and screaming. Fight your way through the cages of the monkey room and push through the final door labeled "Loading Bay". However the bay is now crawling with guards. Eliminate the gunmen in the bay, another good place to use Michael's special ability. Once the area is clear of the guards, follow the green dot that now appears on the radar to the refrigeration unit behind the truck outside. As you approach a cutscene is triggered: Michael gently places the tube into the units holding chamber.
Norton reports that Trevor is on his way at which point you automatically switch to Trevor who is flying a large Cargobob helicopter. Follow the green dot on the radar and maneuver the chopper directly over it; the refrigerator holding the nerve toxin. Once you are low enough and directly above it, a cutscene will trigger. Agent Haines tries to abort the mission as an agency response team is quickly approaching. Trevor and the rest of them need to get away immediately, so to distract the team swiftly coming in, he shoots himself in the leg.
Follow the yellow dot on the map to Trevor's airstrip in Sandy Shores. On arrival, fly directly over the trailer attached to the semi-truck. When the container is centered over the trailer, press the button indicated on screen to release it.
Now land the chopper in the spot marked yellow on the radar. Doing so triggers another cutscene: Dave drives off with the nerve toxin. Michael learns that Lester has settled accounts with Martin Madrazzo, clearing the way for a return to Los Santos. You then auto-switch to Trevor.
Trevor is driving his truck down Calafia Road with Patricia Madrazzo as a passenger. Follow the yellow route to the Madrazzo Estate, La Fuente Blanca. Watch the mission end cutscene as Trevor delivers Patricia back to her husband.
 Conditions for failure
- You die
- Stunner: Stun at least 8 enemies with the Stun Gun.
- Headshots: Kill at least 15 enemies using headshots.
- Accuracy: Complete mission with a shooting accuracy rating of at least 70 percent.
- Mission Time: Complete mission within 13:30.