The machine that transfered his life force to Susan was constructed as
as a capital punishment device. Why not have a story where there is a
criminal too dangerous to imprison because he either can devise a way
out given sufficient time or more urgently he heads up an organization
that will break him out. An organization of either political or
religious fanaticism that could tear apart the galaxy. Susan is in a
position of power and arranges to have the exchange of life force done
using this machine. Most of the story would only have Marcus in
flashback sort of haunting Susan. Well guys, what story can you come up
with to bring back Marcus ?


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