Three explorers returned to Earth after nine long years en route to Proxima Centauri and back. You would have supposed that they would have been greeted as the heroes of the century, feted, honored, rewarded. But Earth was rewarding the trio in a strange and terrible manner-with permanent exile in orbit, never to touch any planet's surface again.
If Earth wanted that crew isolated so badly, it ought to be worth a lot for someone to learn the reason, because the powers that ruled the world were not talking.
The Scorfu -- the Martian equivalent of a Mafia -- had the idea that the three exiles might prove winning pieces in their endless competition with Earth. And therefore the somewhat unscrupulous but absolutely fearless operative, Slade, could be persuaded that the three from Centauri might mean a million for him-Cash on Delivery, Mars.