The arrival of a maintenace shuttle brings an unexpected visitor, Anderson from the failed Clementine mission. Commander McTiernan is concerned as the details surrounding Anderson's mission are vague and his shuttle is registered to a nonexistent company.

A shuttle hit by a meteor crashes into Unity. While crew of Unity have the grim job of recovering the corpses and their personal effects from the shuttle, strange and unexplained events begin happening around the space station.

CALUM is brought to Unity by Professor Jarvis to replace the station's mainframe. In control of the station, CALUM suddenly becomes sentient. Just as quickly, however, it begins to break down, jeopardizing the safety of the station.

The world's last live specimen of the smallpox virus is being transferred to Unity for ""safe"" keeping. Lyle has an crisis of ethics on whether to let such a deadly thing survive. Meanwhile the crew begin to fall ill and it seems their worst fears have come to life.