A mad scientist creates a formula that turns regular bats into giant, killer bats. He uses these bats to seek revenge on his enemies, including a newspaper reporter who is trying to expose his crimes.

Wishing to dispose of his wife, psychiatrist Dr. Elliott makes his patient Nina think that she suffers from a compulsion to kill. He drugs Nina, murders his wife and leaves evidence that points to Nina. The latter, pre-conditioned by Elliott, also thinks she is guilty.