In "The Phantom Creeps" Episode 4, titled "Invisible Terror," Dr. Zorka's malevolent plans take a chilling turn as he employs his invisibility belt to wreak havoc. Government agents and journalist Jean Drew intensify their efforts to stop Zorka, who uses his newfound power to commit crimes and sow fear. The invisible menace presents a unique challenge, adding a layer of suspense to the serial. As Zorka's actions become increasingly unpredictable, the pursuit becomes more perilous. "Invisible Terror" keeps viewers on the edge of their seats, as the battle against Zorka's scientific malice unfolds in this classic 1939 serial.