The Roads Between The Worlds — Michael Moorcock

On Earth-3, one of the fifteen planets occupying different subspacial levels but sharing the name Earth, Doctor Faustaff and his team struggle to save humankind. They must survive the deadly D-squads to save Earth from all the Unstable Matter Situations that are claiming them, one by one.
Elsewhere, the century-old peace in the City of Switzerland is threatened by the arrival of the mysterious Fireclown. The Solar Referendum Party and the Radical Liberal Movement, deadlocked through this time of peace, do not know how to react. Only Alain von Bek and Helen Curtis can begin to understand the Fireclown.
Clovis Becker is the ruler of the daylight side of an Earth that no longer rotates on its axis. With the approach of the end of their 300-year lifespans, the people of this world, these children of the light, face the twilight of their existence.