This is the final quest of the dlc and requires you to confront dr Mobius in the forbidden dome, after you deal with the robo scorpion you confront him and your brain (see Make up your mind for details). Once done return to the Think Tank and confront dr Klein, with a high speech of 75 for the first conversation and science of 100 or mediciine of 85 for the second part you can end this without fighting them unless you prefer to kill them. Once you exit the dome the ending will occur for Old World Blues and your achievement will unlock.