A former Starfleet ensign who defected to the Romulan Empire and later returned to the Federation to help Romulan dissidents.
Stefan DeSeve served as an ensign in Starfleet before defecting to the Romulan Empire, where he lived for many years.
In Face of the Enemy, DeSeve returns to the Federation, surrendering himself to stand trial. He brings Picard a message that Troi has been taken by Romulan dissidents and is part of their plan to smuggle defectors. His growing disillusionment with Romulan society motivates his return, and his arrival is timed to support the dissidents' plan, which depends on the Enterprise meeting the Khazara at the right moment.