Star Trek: The Next Generation – Preemptive Strike [7.24]

Ro, now a lieutenant with advanced tactical training, is tasked to infiltrate the Maquis, whose aggressive actions are threatening to plunge the Federation and the Cardassians back into war.  However, Ro grows sympathetic to the Maquis cause–attempting to protect their way of life from Cardassian harassment after their colony was relegated by treaty to the demilitarized zone.  Ro grows particularly close to a Maquis leader called Macius, and after he is killed she betrays the Enterprise and warns the Maquis of an operation to capture them.