To the dying Arizona town of Abalone comes the mysterious Dr. Lao (Tony Randall) to announce in the local newspaper the advent of his wonderful circus. The editor, Ed Cunningham (Jon Ericson) is engaged in a double struggle: to gain the affections of repressed young widow Angela Benedict (Barbara Eden) and to convince the townspeople not to give up and sell out to cynical local magnate Clint Stark (Arthur O'Connell). Nevertheless, he is also intrigued by the mysterious Lao and his circus, which seems at first to consist only of the doctor, his yellow jackass, and a fish in a bowl — but which hours later has mushroomed into an entire carnival of marvelous exhibits.
Over the next three days the citizens of Abalone have life-altering encounters with the denizens of the circus, which culminate in the spectacle of the destruction of the ancient Atlantis-like civilization of Woldercan, due to its strangely familiar citizens' giving in to the blandishments of a mysterious tempter who strongly resembles Stark. Meanwhile, Stark's thuggish mooks drunkenly attempt to destroy Lao's circus, inadvertently releasing his pet fish/Loch Ness monster, which chases them out of town and is recaptured only with difficulty by Lao and Angela's young son, Mike (Kevin Tate).
The townspeople, shaken by what Lao has shown them, vote not to sell out to Stark — who thanks them for restoring his faith in humanity, and reveals that a new railroad will soon come through, bringing prosperity back to Abalone. With Stark and the town redeemed, and Ed and Angela now safely a couple, Lao's work is done, and he vanishes, only his voice remaining to remind Mike that life itself is the truly wonderful thing.
