With the help of his girlfriend Cathy and Dr. Fong, a psychiatrist, ambitious journalist Johnny Barrett poses as a madman in order to be admitted to a mental institution where a bloody murder has been committed.
A scientist takes the brain of dead man and revives it via electrodes as it lays suspended in a tank of liquid. Soon, the brain grows to possess enormous psychic powers and inflicts its personality upon the doctor who saved it, creating a "Jekyll and Hyde" paradigm.
Captain Hugh "Bulldog" Drummond is called in to solve the murder of a man from whom two lead soldiers were stolen. Drummond learns that the two soldiers were part of a set of thirteen which formed the key to a hidden vault of treasure. Following some clever sleuthing and set-up on Drummond's part, the guilty man is trapped in the vault,which is hidden behind the fireplace.