Elizabeta is starting to lose control. The cops are closing in, her associates are turning states, and the only person left she feels she can trust is Niko. While she is explaining this to Niko, Manny and his camera-man enter and begin to deride her for being a drug dealer. Elizabeta, in a fit of rage, kills them both and asks Niko to dispose of their corpses by giving them to a doctor who deals in black-market organs.
This is a relatively simple mission with a substantial reward. Jump in the car and you will be given a GPS waypoint. Just drive carefully and obey the rules of the road [Stop at lights etc.] as there is no timer you have as long as you need to drive to the doctor. If you take a heavy bump however the trunk will pop open and its contents will be revealed. if at any time this happens jump out and press the LB or L1 to shut the door. Once you arrive, the doctor will inspect the bodies and come up with an alternate cause of death. Afterwards, Elizabeta will call Niko, saying she's cutting off their business relationship as the cops are closing in on her.
An alternative to success is simply dumping the car in the river, but then you don't get paid.