Two hapless freight handlers find themselves encountering Dracula, the Frankenstein Monster and the Wolf Man.
The world of freight handlers Wilbur Grey and Chick Young is turned upside down when the remains of Frankenstein's monster and Dracula arrive from Europe to be used in a house of horrors. Dracula awakens and escapes with the weakened monster, who he plans to re-energize with a new brain. Larry Talbot (the Wolfman) arrives from London in an attempt to thwart Dracula. Dracula's reluctant aide is the beautiful Dr. Sandra Mornay. Her reluctance is dispatched by Dracula's bite. Dracula and Sandra abduct Wilbur for his brain and recharge the monster in preparation for the operation. Chick and Talbot attempt to find and free Wilbur, but when the full moon rises all hell breaks loose with the Wolfman, Dracula, and Frankenstein all running rampant.
- Chick Young [Bud Abbott] and Wilbur Grey [Lou Costello] are working for a package delivery company when Wilbur gets a call from Larry Talbot (Lon Chaney jr) who is in London and tells Wilbur of two large packages bound for Dr McDougol's House of Horrors. One is a coffin containing the remains of Dr Latos/Dracula [Bela Lugosi]; the other is a box with the dormant Frankenstein monster [Glenn Strange]. He tells him not to deliver the crates until he arrives but before they finish their conversation, the moon rises and he transforms into the wolf man and tears up his apartment. Wilbur hangs up the phone just as McDougall arrives about his crates.
At his house of Horrors, Wilbur witnesses Dracula and the monster revive but Chick doesn't.
Dr. Sandra Mornay (Lenore Auburn) invites Dracula and the monster to her castle home on ain island, and tells him she has found the perfect body for the monster's brain - Wilbur.
After being bailed from jail, Wilbur and Chick are visited by Talbot, who tells them he is on their trail and has been following them all over Europe. They don't believe him and he insists on being locked in his room out of fear of transforming.
The next morning, they discover it was Joan Raymond who bailed them out. She's an insurance investigator pretending to like Wilbur in order to get McDougall's exhibits back for him. They arrange to go together to a masquerade ball and go off to pick up Sandra.
Talbot phones the house, and tells Wilbur that he believes they are in the house where Dracula is. Chick with a reluctant Wilbur searches the place but once again, Wilbur sees the monsters but Chick doesn't and still doesn't believe him. While this is going on, Sandra discovers that Joan is an insurance investigator and decides to not go through with Dracula's plan but Dracula bites her and possesses her.
At the masquerade ball, Dracula hides in plain sight as himself, while Talbot changes into the wolf man and tries to attack Wilbur. He ends up attacking McDougall, who believes it was Chick because he has a wolf's mask. Chick runs and hides from the mob while Dracula takes off with Joan and an hypnotized Wilbur but not before Chick finally sees him himself.
The next morning, Talbot realises it was he who attacked McDougall and plans top turn himself in but Chick asks him to help him rescue Wilbur from the castle.
Dracula and Sandra knock out the professor after he realises their plan and proceed with the operation. Fortunately, Chick and Talbot arrive in time to save Wilbur. At the end, the wolfman and Dracula fight, and as Dracula tries to escape in bat form, the wolf man grabs him and jumps into a raging river. The monster pursues Chick and Wilbur but the professor uses fuel to set fire to the pier which attracts the monster and he walks into it and burns to death, leaving only the Invisible Man sitting in a boat with Wilbur and Chick.