Meet with Negotiator is a storyline mission appearing in the S.T.A.L.K.E.R.: Lost Alpha mod and will only be given if the player has joined Duty.

Yes my friend, do you want to deal with Sin? I guess you know they are quite severe guys and trouble us often. They extorted valuable information from us which we need to get back. Petrenko doesn't like it one bit, but their boss suggested a solution : they will send a negotiator who will propose terms for a possible agreement. If we agree to them, they will give us back our valuable information. Can you figure it out, Major, and become our spokesman?
- Voronin