Ol’ Cap Zanser is telling 12 year old Sally Burgess tall tales about Dune Rollers. They are flaming hoop snakes that roll along with their tail in their mouth, taller than a man can reach. Cap attributes the high number of deaths on this island to that fabled creature. The fact that this is called Lightning Island and not Flaming Hoop Snake Island seems to undermine his theory a little.
Sally is going to the dock to meet her father on the boat that identifies as mail. Before she leaves, she hands Sam some rocks she has collected. He is paying her a dime each for these special specimens. He files them away in his special rock file cabinet.
Sally returns from the dock with her father and sister. When Sam hears Sally’s sister Jean is coming he frets about his appearance and says he would have changed his shirt. In a fitting microcosm of the times, Jean walks in with her arms full of groceries and her father walks in with an armful of science books. Maybe Sam wanted to change his shirt so she could wash it.
Sam shows Dr. Burgess his rocks and is stunned to see the two rocks that he filed have fused into one pointy stone, and that the weight is now double the two stones combined. Burgess theorizes that the stones are a mineral from a meteor. The fragments are trying to recombine into the original rock.
Jean calls Dr. Burgess and Sam to dinner. Sam says he needs to change his shirt. This guy goes through shirts like Bruce Banner. Dr. Burgess goes to check on the rocks before dinner and Jean tells him to get to the table. She calls him Carl so maybe I have misjudged their relationship.
After dinner, they go to check on the rocks. They find that two stones have burned their way out of the cabinet, fused together, and burned their way right through the front door leaving a scorched cutout like Speedy Gonzalez. Later that night, Cap is attacked by the flaming stones and killed.
Instead of the usual commercial for Kreisler Watchbands, this episode has a bizarre break where a man gives the mission statement of the series. “The stories may seem improbable but are they impossible? Nobody really knows. We do know the universe that surrounds us is an enormous mystery. Our stories try to break through the barrier of life as we know it through discovery and our imaginations what life beyond may be like.” And if you understand that last sentence, you should be working for the NSA.
Dr. Burgess and Sam find Cap’s body and assume he was killed by lightning. Sam says he looks like the “Japs” he saw in WWII who had been hit by a flame-thrower. They realize that these rolling stones are the mythological titular dune rollers. Dr. Burgess plans to blow up the main stone, but Sam volunteers to take that risky assignment so Burgess can get the girls off the island.
It isn’t even clear what this is supposed to accomplish. Is he intending to blow up the main rock? Wouldn’t it just reassemble? And why did he drop some stones at the blast site? Was it to lure the master rock? But the smaller stones seek out the big rock — the big rock isn’t like Uber conveniently picking up the kid rocks.
But the bigger mystery is why this young girl is living on a remote island with Sam and Cap. At least Jonny Quest had his dad to keep an eye on Race Bannon.
The very end should have had one of those horror movie question marks at the end. We pan to see a glowing dune roller. But is it a large fragment from the blast? Is it another one? The last shot is bizarre and difficult to describe. It is not just a zoom-in on the rock — the soil below it is moving. I think they were trying to create an illusion that it was growing. It is pretty clever, but doesn’t work today. On a fuzzy 1952 RCA, who knows? 
-  Actually, the lousy YouTube version might be a good 1952 RCA emulator.
- Bruce Cabot (Sam) starred in King Kong. No, the other one. Before that.
- Sally is played by Lee Graham and is clearly a young girl. Graham’s other IMDb credits include Storekeeper, Marine, Titanic Lookout, Crew Chief and a few more androgynous roles. Back then these would have been traditionally male jobs. If this were 50 years later, I would get it, but in the 1950’s, I can make no sense out of it.