Two astronauts, Mac McKenzie (Frank Aletter) and Hector Canfield (Jack Mullaney), travel faster than the speed of light, resulting in being sent back in time to prehistoric days. There, they have to adjust to living with a cave family led by Shad (Imogene Coca) and Gronk (Joe E. Ross). (Coca's character's name was originally pronounced "Shag" in the first episode, after which her character's name was pronounced "Shad" (evidenced in the rerun episodes on Antenna TV), though in the opening titles, her billing still read "IMOGENE COCA as SHAG"; this changed in the episode "20th Century Here We Come" when new opening titles were created for the series' retooling and her billing was changed to read "IMOGENE COCA as SHAD". Their children were 18-year-old Mlor (Mary Grace, credited in the retooled closing titles as Mary Graham Grace) and 14-year-old Breer (Pat Cardi). The chief of the tribe, Boss (Cliff Norton) and his right-hand man Clon (Mike Mazurki) were always suspicious of the astronauts.
Ratings were impressive for the first few weeks on the air, but they soon plunged. Show creator Schwartz came to the conclusion that three factors were the cause of the decline in audience interest:
For these reasons, after 18 broadcast episodes set in prehistoric times, the series was retooled beginning with the January 22, 1967 episode. (A 19th "prehistoric" episode had been completed, but it was not broadcast until after the end of the series' original run; this could possibly have been due to its originally scheduled broadcast being preempted for special programming, which happened occasionally to many TV shows, throwing their original broadcast order out of sync when the networks would broadcast the episode at the end of the season's first-run episodes rather than postponing the broadcast until the following week.)[original research?] Essentially reversing the premise which had been followed the first half of the season, on the January 22 episode, the astronauts repair their space capsule and return to 1967, with Shad, Gronk, and their children in tow. Boss and Clon make their final appearances in this episode, which also introduces two new supporting characters who would stay with the show going forward: Alan DeWitt as Mr. Tyler, manager of the apartment building where Mac and Hector live, and Frank Wilcox as General Morley, their commanding officer.
In the retooled version of the show (which had an updated theme song, explaining the new premise), the prehistoric family must begin adjusting to life in the 1960s, reacting to the unfamiliar surroundings, and setting up home in 20th-century Los Angeles. For example, one episode had Gronk and Shad learning to write their names and signing them for many salesmen who brought "presents", which had to be paid for later. Mac and Hector also had to convince their disbelieving superior that they really did travel in time, and are not playing some sort of elaborate practical joke. Seven episodes were produced with this new premise before the series was cancelled at the end of the season.