Entry to Elsewhen

The plague defies all efforts to treat it or stop its spread, showing varied symptoms in different victims and mutating rapidly.

Also, the plague seems to be spread by multiple "Typhoid Marys", found unconscious on trains with large amounts of cash but no identifying information.

Eventually it is discovered that the plague is being spread by human military forces who have travelled through time from several centuries in the future.

The plague's effectiveness derives in part from atrophied immune systems resulting from long-term prevention of exposure to any infectious agent.

This story takes place aboard a multi-generational spaceship travelling from Earth to a planet orbiting Tau Ceti with the goal of establishing a colony.

Additionally the idea causes severe agoraphobia, as experienced by one Tripborn crew member who makes a landing on the planet and must be retrieved by remote control.

The Earthborn crew members employ a variety of means to make the Tripborn less comfortable on the ship, such as Psychoactive Drug included in the food supply and subtle background sounds designed to cause unease.

Since the ship's cargo includes the necessary tools to build a city suitable for 10,000 inhabitants on the destination planet, the Earthborn crew suggests that they instead be employed in the construction of a second spaceship.