After having dinner with Fred's father, Ed, and Barney's parents, Bob and Flo Rubble, Fred and Barney wanted to see their grandchildren, Chip and Roxy, but Pebbles was unavailable for reasons that she would not explain. The four of them were thus persuaded to stay in a motel just outside Hollyrock.

"Why on earth would Pebbles not tell us what she's up to?" asked Wilma.

"She's probably planning a surprise for us," yawned Betty.

"A surprise?" asked Barney. "What could it be?"

"We'll find out," said Fred, "but I won't give any hints because that would ruin it."

The next morning, they found out that she had returned with Bamm-Bamm and, much to Fred's disgust, Pearl Slaghoople, who had come from Bedrock™ to see her great-grandchildren. Fred and Barney were just about to set off on their way to Mt. Goldrock when a rock flew into the house and injured Wilma's foot.

Pebbles picked up the rock and saw the letter "S" chiseled on it. "It's something foul," she said, "but what could it be?"

"It's the work of Dr. Sinister," said Fred. "We gotta stop him!"

Fred and Barney ran off to expect some danger, but they found none until they turned their backs. Two thugs kidnapped Pebbles and Bamm-Bamm, almost certain that they knew something about the treasure.

"I'll deal with Chip and Roxy," said Mrs. Slaghoople, who was in no mood to chase after the two thugs. "It's not something to do at my age."

"It doesn't matter, Madam," said Betty nervously. "We'll get our children back before you know it!"

"Enlèvement! Enlèvement!" Wilma shouted. Thankfully, they ran into Mr. Slate, who had taken French lessons in school, watching them race by.

"Whose kidnapping are you talking about?" he asked. "With such action as this, Flintstone, you'll never have a dull moment in your life."

"Two fiends ran off with our children," explained Fred, showing him the map, "and yes, I haven't had a dull moment since I found this map at the quarry."

They found an eerie Petro-Gothic castle in Hollyrock, and despite the cinematic industry around it, this castle was no prop. "That's Dr. Sinister's castle!" cried Barney. "They must be trapped inside!"

"The trouble is that we can't get in," said Fred. "Dr. Sinister's doors to the castle are unusually voice-activated, and they will only open if he says anything."

Just then, from the highest and northernmost turret, Dr. Sinister looked out. "You fools!" he shouted, causing the front door to open.

"Run for it!" thundered Wilma, and they all rushed in. Barney found a torch and, presumably against the will of the castle's owner, grabbed it.

"This place scares the hell out of me," said Betty nervously.

"Oh, boy," said Barney as he looked around at the creepy stuff in the castle. "Count Rockula would love this place."

"I wish we knew how to get through this place," said Fred, who quickly realised what he had said.

Suddenly a green alien popped up out of nowhere. "You wished, Masters?" asked he.

"Not that we sought your assistance, Gazoo," said Barney, "but we really must save Pebbles and Bamm-Bamm before it's too late!"

The Zetoxian placed a tracking device in Fred's hand. "This will aid you in your journey," said the Great Gazoo, "but it will only work for a short time."

Up the stairs the five of them went. Finally, they reached Dr. Sinister's lair, where two cells stood. In the left cell were Rupert and Madame Hexenstein, and Pebbles and Bamm-Bamm were in the right. Fred wanted to snatch the keys on the table, but before he could…

"Not so fast, Flintstone!" cried Dr. Sinister. "You've foiled me twice before, but this time I will reign supreme."

"We'll see about that," said Wilma. "I don't care if you feed Fred or Barney to the piranhas."

"I have creatures much, much worse than that," said Dr. Sinister, escorting them to a pool of drab green monsters with sharp, pointed fangs and long tongues. "These are anthropophagosauruses, and they can strip a basketball player down to the bone in ten seconds." The four of them were then taken to another prison cell where Dr. Sinister locked them. Now after all his effort to get the treasure, Fred felt as though he had lost all hope… but he hadn't.

"I wonder where Gazoo is," sighed Barney sadly.

"I'm right here," said Gazoo outside the bars. "How may I help you?"

"We really need those keys," said Fred. "What do you have, Gazoo?"

"Open your hands and close your eyes, and I will certainly help you guys," said Gazoo, placing a ring in Fred's hand. "It's a magnetic ring, capable of deflecting a compass needle, yet precise enough not to attract the iron bars that hold you."

"Thanks, Gazoo!" cried Fred as he put the ring on and Gazoo disappeared. No sooner had it slipped on his hand than the keys began shaking. Fred lifted one of the keys, and it fit exactly in the hole, turning his hand to unlock the door. He then used the ring, still in his prison but with the door unlocked, to move the keys toward the cell where Pebbles and Bamm-Bamm were.

"We're free!" shouted Pebbles. Fred, leading the others out of his cell, tried moving the keys to the chamber with Rupert and Madame Hexenstein, but Bamm-Bamm had beaten him to it, bending the bars in the cell with his Herculean strength.

The only way to cross the anthropophagosaurus pool was a small bridge that Dr. Sinister could rotate with two small buttons on each side. Pebbles and Bamm-Bamm had just crossed the bridge when Dr. Sinister began chasing their fathers. Wilma and Betty also crossed the bridge with Madame Hexenstein when they came up with a plan.

"I know exactly what we should do," said Wilma. "We need Fred and Barney safely on the bridge, and then we'll push the button."

Fred escaped and got on the bridge safely, followed by a much exhausted Barney. Dr. Sinister soon got too busy chasing Rupert when he realised where Fred and Barney had gone. He approached the bridge.

"Now!" yelled Fred and Barney collectively, and Betty pressed the button to rotate the bridge. Dr. Sinister soon found himself separated from his prey and challenged Betty to a game of spin the bridge. On Dr. Sinister's end, the button quickly malfunctioned, so he tried running onto the bridge himself. Unfortunately, it was too late for him, and he landed in the anthropophagosaurus pool, where the hideous fiends devoured him until only his glasses remained.

"Enjoy your dinner," smirked Fred. "You deserve it."

By now, Betty's fingers were getting quite sore, so she stopped the bridge perfectly as it had been before the commotion. Rupert held the torch that Barney had carried and luckily placed in a holder before being locked up.

"May the light shine always on you, Flintstone," said he, "for once again, your courageous actions have overcome many perils."

Barney led the other seven people down the stairs, again holding the torch as he had done before. When they reached the bottom, Barney unknowingly lit one of the curtains on fire. None of them knew it, however, because they were glad that they had defeated Dr. Sinister for good.

As they all marched triumphantly away from the castle that soon was to be no more, Fred exclaimed "YABBA-DABBA-DOO™!"