The Double Kill is everything you want in a thriller, it's clever, twisted, imaginative, it features the perfect game of cat and mouse, and of course there's a fiendishly clever twist waiting for you, one that I certainly didn't see coming.
Series five has been fantastic, The Double Kill is certainly up there with if it's a man hang up, and I would say deserving of the classic status.
The writing is tight and clever, as mentioned it's similar to a very famous plot, Dial M for Murder, but of course Brian Clemens manages to put his own expert spin on it.
Very well produced, it looks and sounds great. Excellent acting also, Gary Collins and Peter Bowles are superb.
It's a classic, I can't give it the perfect ten, as the plot is virtually a carbon copy, but it is a virtually perfect thriller, 9/10