From the Chaosium website:
This is a convention scenario with highly detailed characters and handouts intended for a theatrical style presentation in a single long session.
The Arrival
Six days ago the hammer fell. The red comet did not strike the planet, but it was a near miss. Fragments smashed into the earth bringing tidal waves, storms, and fallout. This was a rage of elemental destruction that devastated most of the planet. Millions, perhaps even billions, have died.
The main mass of the comet seems to have entered regular orbit. A red eye rises at night and glares balefully through an occasional rent in the near perpetual cloud cover: a hellish new moon added to the sky. Communications are out. Who knows what is happening out there?
It seems like you will be on your own for some time.