In the future, mankind lives in vast underground cities and free will is outlawed by means of mandatory medication that controls human emotion. But when THX 1138 (Robert Duvall) and LUH 3417 (Maggie McOmie) stop taking their meds, they wake up to the bleak reality of their own existence and fall in love with each other in the process. But love is also illegal in this Orwellian dystopia, and the act of making love has made both of them outlaws on the run from an army of robotic police.