Speaking to Zap2It, Nix explained that Michael (Jeffrey Donovan) will have an important meeting in the first episode.
"[At the end of the last season] he was led into a prison facility of some kind, and so he's in a room in that prison facility," he said.
"He's meeting someone there. And the character that he meets is played by Robert Wisdom who is sort of the new face of the people that burned him."
He continued: "[Michael's] had a lot of adversarial relationships, whether it was Tricia Helfer's character Carla or Michael Shanks's character Victor or with John Mahoney's character Management. He's had a lot of people threatening him. And then along comes Robert Wisdom's character, whose name is Vaughn, and he's a different guy. He's a reasonable man."
Nix added that Michael will be forced to decide whether to start working with Vaughn.
"[Vaughn is] presenting Michael with a bunch of reasonable propositions and proposes a new relationship," he said. "And Michael warily accepts. And so that's sort of what kicks off the season."
Burn Notice returns for its fourth season tonight at 9pm on USA.