What is at the heart of the criminal mind? That's what Dr. Stander (Irving Pichel) wants to find out. To do that, he signs up a bunch of hardened criminals for a one-way cruise. The captain (Lyle Talbot) thinks thatthe doctor is well-meaning in his desire to unlock the mysteries of the criminal, but when he discovers the true nature of the doctor's horrific experiments, he takes a stand. Now it's the captain, his crew and the criminals against the doctor and his henchmen in a high sea battle like no other.