Dr. Patrick "Pat" J. Cory is researching brains with his assistant and friend Dr. Frank Schratt and his wife Janice Cory through experiments with monkeys in a laboratory in his house.
Dr. Henry Jekyll experiments with scientific means of revealing the hidden, dark side of man and releases a murderer from within himself.
The wife and mistress of a loathed school principal hatch a plan to murder him while having the perfect alibi. They carry out the plan...but then his body disappears.
A scheming widow hatches a daring plan to get her hands on her late husband's inheritance, unbeknownst to her that she is targeted by an axe-wielding murderer who lurks within the family's estate.
