What is the main conflict in The Sirens of Titan by Kurt Vonnegut?

Sirens of Titan tells the story of the wide-ranging journey of Malachi Constant, the wealthiest man on Earth, from Earth to Mars to Mercury, back to Earth, and finally to Titan, a moon of Saturn. Along the way, Constant is seemingly manipulated and controlled by Winston Miles Rumfoord, an American aristocrat whose existence has been scattered across time and space after flying into a warped region of the solar system while on a space flight to Mars.