Sentenced to life in prison for a crime he (mostly) didn't commit, Darien Fawkes was transfered from jail to a laboratory when he agreed to be a guinea pig in a secret, government experiment. Because Darien's own brother was the head scientist in the experiment, Darien believed he was basically safe. (Of course, the brother got killed off in the pilot). A gland that secretes a mysterious substance-- Quicksilver -- was implanted at the base of Darien's skull. The Quicksilver secretions enable him to become invisible at will, but they unexpectedly also degrade his higher brain functions, unleashing his dark impulses and pushing him towards insanity. Claire, the lady who "maintains" his health (The Keeper) calls this effect "Quicksilver Madness". Darien has struck an uneasy deal: the counteragent (which restores a balance) in return for serving a clandestine government agency as an operative. His boss is a secretive type called "The Official", and their agency is nominally listed under The U.S. Dept. of Fish and Game. His sidekick is an agent called Bobby Hobbes, who is a suspicious, cynical ex-FBI agent, now working for the low-rent" "Agency", not entirely gratefully. Lots of humor and entertaining scripts!! Though the show is now ended, it went out on a happy note, and it was a refreshing change from a show getting yanked with no resolution of story lines! I'll miss Darien and the gang!
