Rik had been psycho-probed and his memories destroyed. Now he was only a helpless field worker in the kyrt fields of Florina, where every human being was owner, body and soul, by the ruling world of Sark. But slowly his memories began to return.

He knew he had once studied the thin currents of space and that some terrible danger threatened the sun of Florinna and Sark.

On Sark, the Ambassador of Trantor was searching for him and his dread knowledge. But the Squires of Sark wanted no warning to upset their wealth-producing monopoly on the sale of kyrt.

Somehow Rik must warn both worlds before all life was destroyed. But what could a serf do against the power of distant Sark?