An international prize is offered to the first man to complete an interplanetary journey. For British pilot Dale Curtance, it is the ultimate challenge; he must build a ship, assemble a top-notch crew, and beat the Russians and the Americans, too. Soon the Gloria Mundi heads for Mars. There's only one problem: a stowaway named Joan Shirning. At first, the men resent Joan's presence. But they come to realize that she is the only one who has firsthand knowledge of the Martians--or at least the intelligent beings that will one day replace them.