Jobs are scare after the Bowery Boys--Slip, Sach, Bobby, Whitey and Chuck--graduate from exterminating school, and when the Brown Realty Company hires them to exterminate the Menlo estate, the boys eagerly set off, undeterred by rumors that the place, which was formerly owned by a magician, is haunted. They almost change their minds when they arrive, however, as the house is dark and is located next to a graveyard. Inside the house, the boys are frightened by mysterious happenings such as lights that turn on at odd moments, pictures that move and strange messages that appear on the walls. Unknown to the boys, the house is being used as a hideaway for Dr. Coslow, who, with the help of his prisoner, Dr. Bender, plans to transplant a human brain into a gorilla. The boys receive extra help when Gabe, who has returned from the Navy, arrives with his French wife Mignon. Sach disappears when he plays a tune on a piano, which causes the wall to rotate. Then, Mignon is captured by Coslow's men. While Coslow watches on closed circuit television, the boys search for their two missing friends. Meanwhile, Mignon and Sach both discover that Coslow has built a laboratory in the basement, whose entrance is located in an outside grave. Coslow decides that Sach is the perfect person for his experiment, but before he can carry out the operation, Slip accidentally finds the laboratory as well. With Dr. Bender's help, Slip slows down Coslow's men by dousing them with ether. The rest of the boys eventually break through the ceiling into the lab and attempt to subdue Coslow. In the meantime, one of the gang who has gone for help, finally returns with the police, who round up Coslow and his men.