Case History: Daphne's Uncle John, a film director, has hired the gang as extras on his new film, The Ape Man of Forbidden Mountain, after the superstitious locals refuse to go on the set: the story is based on a real legend about an ape man that burned down a local mansion. Filming begins with a shot of the star, Candi Mint, standing on a rope bridge and being menaced by the Ape Man, played by Carl the stuntman. But when the ape-like figure begins shaking the bridge, it becomes apparent that she is confronting the real Ape Man. Scooby runs out on the bridge and drives it off. They find Carl locked in a trunk, and both he and Candi quit the picture until the Ape Man is caught. The gang decide to investigate.

They search the set, which is full of traps and hidden panels: while looking at a script which someone has left open to the bridge scene, Freddy disappears behind a trapdoor while Scooby encounters the Ape Man behind a phony mirror. Scooby drives the Ape Man back up the stairs, but they lose it in the darkness on the second floor. Playing with switches while trying to find the lights, they open a secret passage under the stairs and find Freddy, who has found a ready-made trap in the basement. Scooby and Shaggy go out to act as bait for the Ape Man and find him in the billiards room. But when they lure him back to the basement, Shaggy gets caught in the net instead and the Ape Man disappears through another secret passage behind a wine cask. This passge leads from the film set to the star trailers. Searching the trailers, Shaggy chances on an insta-camera and is able to snap a picture of the Ape Man with his mask off.

The Ape Man chases Shaggy and Scooby, who lead him back into the film set mansion and into a trap. He is unmasked as Carl, who, resentful at not getting the lead in the picture, had decided to sabotage it.

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