Spaceships, including the Jason, the Starbird and the Invincible, had disappeared into hyperspace - never to return. Everyone assumed that their disappearances were due to mechanical failure. But then the Invincible was found deserted, drifting in space, six months after vanishing. The ship's engines were undamaged, the hull intact - but there was no sign of life aboard - no trace of its crew or the two hundred passengers. What had happened? Was it something or Somebody out there in hyperspace?