Synopsis by Hal Erickson
In the third episode of the six-part story "The Sensorites," the Doctor (William Hartnell) and his companions are still the prisoners of the Sensorites, a dying race of telepaths. A new and unexpected enemy arrives on the scene to further imperil the TARDIS crew. And as if that weren't enough, Ian (William Russell) makes an error that could prove to be fatal. Written by Peter R. Newman, "Hidden Danger" originally aired on July 11, 1964.