A human scientist capable of living underwater discovers similar alien life inhabiting human bodies, and looks to them for a clue to his origin.
| 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 |
 Tiffany BollingLioa / Dilly | Lioa / Dilly |
 Annette CharlesGinny Mendoza | Ginny Mendoza |
 Burr DeBenningXos / Chazz | Xos / Chazz |
 Stanley Bennett ClayBoy | Boy |
| AAlan MandellGrant Stockwood | Grant Stockwood |
| HHank StohlSub Captain Wes | Sub Captain Wes |
 Russell ArmsMedical Examiner | Medical Examiner |
| AArch ArchambaultSecond Officer | Second Officer |
| MMichael J. LondonAir Lock Man | Air Lock Man |
| VVince Deadrick Sr.Herb Wayland | Herb Wayland |
| MMaurice HillLou | Lou |
| JJoel LawrenceHot Tub Manager | Hot Tub Manager |
| MMaralyn ThomaMyrtle | Myrtle |
 Dick WinslowFish Store Clerk | Fish Store Clerk |