Sixty young trainees of the Planetary Survey Service disappear, along with their instructors and ship, as unknown aliens with advanced weaponry attack the settlement of New Finland

It was just as the League had feared. The disappearance of Mac Larson's Survey Service training ship, the VENERA, had been engineered by the Guardians. Mac and Joslyn's fellow Survey recruits were captive in enemy hands - and forced to lend their expertise to the Guardian's plan for total conquest. In their first encounter, the League had vanquished the Guardians. But now the enemy had a new ally - an alien race whose biological weapons were as deadly as they were invincible...