The Cetacean is called upon to recover a space probe that crashes in the sea, and Mark soon learns that the probe is covered with thousands of tiny alien beings. They intend to learn all they can about the human race by invading host bodies and controlling them. Mark must return them to space before they destroy all humanity.
| Actor | Role |
|---|---|
 Patrick DuffyMark Harris | Mark Harris |
 Belinda MontgomeryDr. Elizabeth Merrill | Dr. Elizabeth Merrill |
 Kenneth TigarDr. Miller Simon | Dr. Miller Simon |
 Alan FudgeC.W. Crawford | C.W. Crawford |
 Fred BeirCaptain Bracy | Captain Bracy |
| BBrad DavidSid | Sid |
 Carole DemasPamela | Pamela |
 Ivan BonarEdwin Shirley | Edwin Shirley |
 James B. SikkingColonel Manzone | Colonel Manzone |
 Erik HollandNot listed | Not listed |
| JJames R. ParkesNot listed | Not listed |