Chuck Spillers (Cox) has just been released from prison, much to the joy of his devoted wife Annie (Donnelly). Chuck had been regularly visited by a mysterious benefactor during his stint, pet shop owner Martin Blueck (Cushing).

Going to thank him for his generosity, Chuck is offered a job to maintain the exotic animals that Blueck keeps caged in the back of his shop.

But “caged” isn’t quite the proper word. Blueck uses a high electric current to condition his beasts, a fascination that he obtained during his time at a concentration camp. Chuck goes along with the job, but the lure of a safe awakens his old thieving habits.

Too bad the intended break-in leads Chuck straight into a metal cage beneath his feet. Now he is just another one of Blueck’s animals, a mere electric shock away from turning himself into burnt steak. Will Chuck ever escape his crazed captor’s clutches?

An ace script and game performances by the cast make this one of the best overall entries of the series. Writer Francis Essex digs into the theme of using fear as a conditioning tool to great effect, peppering the tale with just the right amount of social commentary to retain its timeliness.

Cushing is magnificent, as always, displaying his trademark skill of playing the sweet, gentle old man and turning into the cold sadist on a dime. The chemistry between Cox and Donnelly is superb as well, the frustrations and collaborations of a married couple coming through in their performances wonderfully.

It all unfolds at a gradual, calculated pace that ends with a damning conclusion in which nobody wins. And it shows that the most terrifying scream is the scream that can never be heard.

A knockout.