This has always been my favorite episode of this TV series - the one that unsettled us all on Saturday nights in the latter months of 1980.
Having Peter Cushing onboard for this story as the disturbing Blueck is a real boon - as well as future film star Brian Cox, in an early role as former safecracker Chuck Spillers.
With Chuck released from prison and reunited with his wife Annie at their remote cottage, life at last feels sweet again for the couple.
But, during his stay in prison, he'd received visits from elderly and mysterious benefactor Blueck and, when the old man offers him a job minding his pet shop while he's away for a few days, Chuck is more than happy to accept.
The only problem is, Blueck has a huge and secret menagerie of caged wild animals hidden in his basement for Chuck to take care of. It seems Blueck is keeping them there to conduct cruel and nasty 'experiments' in their behavior - training them to live in fear of (and respond to) bells and buzzers.
The only problem is, do his experiments actually end there...
This is an excellently played and tense episode from start to finish - not to mention a rather uneasy watch for animal lovers such as myself!
Cushing excels as the creepy and crafty Blueck - emotionless, cold, and obsessed with his crazed experiments, but giving the air of a kindly pet shop owner to the outside world.
As often in these kind of stories, the local police are pretty clueless and indifferent - so it's left to Annie to use her ingenuity when her husband's disappearance is somehow linked to the pet shop.
This one really keeps you on the edge of your seat and guessing till the end - and the actual ending is pretty unexpected too.
In all in, a memorable, disturbing and highly-original story from this excellent series, and one that leaves a lasting impression.