While investigating the disappearance of the U.S.S. Drake on the planet Minos, the crew battles aggressive energy spheres, swallowing sinkholes and invisible attackers.
Arriving at Minos, the crew is met by a prerecorded sales pitch for highly-advanced weaponry. This is not surprising, however, since the Minos people were renowned arms dealers during the Erselrope wars.
While exploring the planet Riker, Data and Yar are attacked by an energy sphere. Lieutenant Yar destroys the sphere, but not before it traps Riker in a transparent cube. Then, after Picard and Dr. Crusher beam down to investigate the crisis, the ground swallows them into a subterranean cavern, seriously injuring Dr. Crusher.
Although Data is able to free Riker, the away team is unable to locate Picard and Crusher. Meanwhile, the U.S.S. Enterprise comes under serious attack by an invisible enemy, which La Forge desperately fights to contain. Until the ship can adequately defend itself from the attacker, La Forge cannot beam up the crew members on Minos.
Back on the planet, Data finally locates Picard and Crusher. The team discovers that the attacks are coming from a computer-generated weaponry system which has gone out of control and has destroyed the civilization that created it. Fortunately, the team is able to turn the system off in time to save the planet ... and themselves.
Onboard the U.S.S. Enterprise, La Forge is able to destroy the invisible enemy and beam Picard, Crusher, Riker, Data and Yar aboard.