When Diana seals off the Open City with an impenetrable force field which destroys humans on contact, Donovan and Ham must kidnap the alien genius responsible for its development.

With a blood sample from the "star-child," Diana creates an uncontrollable and deadly clone which seeks out Elizabeth; Bates tests Julie's loyalty when he suspects she is sympathetic to the Resistance whose headquarters he is preparing to destroy.

While Bates remains in a coma Charles plots to overthrow him, elsewhere Willie is gravely wounded so the rebels kidnap a medical student of the Visitors.

Sent to investigate Charles' death, newly arrived Inspector General Philip allows Lydia to choose a trial by combat in a laser duel to the death with Diana.

Needing medicine to treat a deadly diphtheria epidemic, Julie and Kyle recruit a youth gang, one of whom may be a Visitor spy, to help steal the serum.

When Philip and Diana install a high tech computer capable of launching a final victory over Earth, the Resistance's only hope at retaliation is a teenaged computer whiz.

The Leader stuns the Visitors by ordering a truce and traveling to Earth to negotiate peace; Diana plots to disrupt the peace.