The Invisible Man

Going to Mexico to investigate Arnaud, Bobby meets his new partner Bobby Hobbes: a veteran spy and near basket-case. They escape an ambush by French-Canadian spies. Meanwhile, Arnaud has had Darien's girlfriend Casey brought down to Mexico, planning on using her as a hostage. Darien goes to rescue her, prepared to kill Arnaud since Darien thinks he'll be going insane shortly. Arnaud plays his trump card: there's a counter-agent that will stave off Quicksilver madness, and he'll give it to Darien if he works for him. Darien refuses, escaping with Casey and blowing up the compound (although Arnaud escapes). Both the counteragent and the formula are destroyed, and Darien goes to visit his brother's grave one more time before going permanently insane. However, the Official meets him there and reveals that his Agency was working with Kevin, and they have the counter-agent as well. As long as Darien works for them, he'll get regular doses of the Counter-Agent. Reluctantly, Darien agrees.