David is lured by his new girlfriend Lorlei to her Uncle Count Dracula's castle near the swamp on a thunderous night. While there, David becomes spooked by some of the surroundings including a moving armor, a painting of Count Dracula on the wall (which is really The Count standing behind a blank picture frame) and a bat-type lamp and tries to exit. Lorlei manages to persuade him to give her a kiss and ends up paralyzing him with a magic necklace she places on him. Soon The Count decides that David is the perfect specimen for Dracula reborn!
Meanwhile back at The Monkees' pad, Micky and Peter begin to worry since David isn't back yet so Michael calls the castle. But when he receives The Count's creepy laughter on the phone, he's convinced that David is in trouble and needs their help; while Micky and Peter hide under a sheet Michael declares that once again Courageous American Youth leaps into the fore..."or five!" At the castle, Dracula starts training David on how to act a vampire by having him drink tomato juice as blood and flying lessons with a vampire's cape. Michael, Micky and Peter arrive at the castle to rescue David where The Count welcomes them inside but Micky is reluctant until Lorlei invites them in. They bring them to the library where they inform the guys that their mate went into town and should be back soon before excusing themselves. The guys start to get spooked by their surroundings while The Count and Lorlei observe and take notes behind the picture frame on the wall. Then Count Dracula decides that Peter's mind would be perfect for the monster since he doesn't have a brain in his head! Michael reads a book, A Study Into The Nature Of The Vampire by Count Sylvanias Dracula, and they notice the picture of the vampire in the book resembles The Count. They deduce that The Count and Lorlei are vampires, and Michael and Micky search for David while Peter stays behind.
David, chained to a wall in the cellar, tries to turn The Wolfman against The Count by accusing him of keeping Wolfman in the basement all the time, not giving him second billings in the pictures they've made together and exploiting him. When The Wolfman prepares to pounce on Lorlei, David informs her that the Wolfman wants a better percentage of the profits, cookouts on weekends, and the right to play his own music and Lorlei agrees. Later, Lorliei seduces Peter in the library into kissing her freezing him with the magic necklace like she did with David. The Wolfman enters and attempts to carry Peter off to dispatch but is stopped by The Count who manages to distract him with links of hot dogs. Then The Count and Lorlei take frozen Peter to the lab. Michael and Micky continue to search for David when they briefly encounter The Mummy. Micky is still spooked by their surroundings and is ready to leave but Michael insists on finding David and they head back to the library where they discover Peter is gone, too!
Michael and Micky continue their search, neither of them noticing that The Wolfman is behind them. Soon Michael finds a secret passageway and enters it but Micky doesn't follow him in and when he spots he Wolfman, he runs back to the library and barricades himself in with furniture--which is exactly where Loreli uses the necklace on him just as she did with David and Peter, and promises The Wolfman that Micky is for him, and Wolfman arrives with a banana. Michael finds himself in the cellar but he becomes scared when he realizes that Micky is not behind him. He's further scared when the comes across The Mummy in his tomb and heads back upstairs and into the library where he hides from The Count and Lorlei behind the picture frame in the wall. There, Michael overhears and takes notes as Dracula and Loreli plan to switch brains from Peter to their monster, in the underground crypt at the height of the full moon at midnight!
Meanwhile, in the dungeon, David and Micky, in chains, are faced with the possibility of becoming monsters. The two become Count Dracula and The Werewolf in a fantasy sequence, but their fantasy is interrupted by The Count. Dracula commends the boys on their conversion to monsterhood, but they try to kick him out for interrupting their fantasy sequence and he's not allowed to take part in same. But The Count informs them that he controls everything including their fantasies, and to their shock they really have become a vampire and a wolfman when they can't take their makeup off! The Count orders the Wolfman to chain them back up as he and Lorlei prepare for the operation on Peter. Michae makes it to the cellar and hides in the Mummy's tomb with The Mummy as The Count arrives. The vampires and Wolfman drag two stretchers of Peter and the monster covered with white sheets preparing for the operation. Nes switches wardrobes with the Mummy and arrives as his assistant and manages to trick The Count with a scalpel and a chisel, snatching the stretcher right under his nose and takes off. Then Michael frees Werewolf Micky and Vampire David. Realizes he's been duped, The Count decides to use mind control on the guys which makes Micky try to bite Michael's hand and David bite his neck and drink his blood. The Count finds the boys have their monster while he and Loreli have Peter and throws an energizing switch, setting off a wild romp between monsters and Monkees as they fight off Frankenstein's monster, Wolfman, Dracula and The Mummy singing "Goin' Down", eventually defeating them all.
Returned to reality, The Monkees reconvene in the library, where Michael reads in the book that defeated monsters can't return for a thousand years. They are all relieved that they're no more monsters until the book starts flying in space which spooks Peter thinking it's The Invisible Man. Mike reveals it's merely special effects with a wire holding the book up and proves it by using scissors to cut the wire. David uses the scissors as well and manages to cut the wire causing the book to drop on Peter's foot.