A computer virus that began on an ancient ship spreads through two fleets.
The Enterprise races to the Neutral Zone to help the starship Yamato, whose captain was an old friend of Picard, and finds the ship destroyed. The Enterprise's own computers soon begin to fail in strange ways, caused by an alien computer virus transmitted from an ancient system on the planet Iconia.
The story builds suspense as the crew becomes cut off from their own systems while the Romulans close in nearby. The Iconians and their gateways were an idea of a long-vanished civilization of great power, and the idea returns in a later series. The episode is a tense look at how dependent the crew is on technology and is a well-regarded high point of the second season.