Lt. Weigand and the Norths become trapped in the rural home of Dr. Arno, a physician treating a homicidal maniac who’s hiding somewhere in the house. The group stages a fake murder scene, hoping the mysterious “Patient X” will be drawn into the open. Instead, when the lights are lowered Dr. Arno’s secretary is actually stabbed to death. Once Weigand learns the actual name of the patient, he makes some phone calls and learns they’re deal with a real-life Jekyll and Hyde.