I agree that there are certain weaknesses to the endings of "Murder by the Book" and "Any Old Port in a Storm," but in my opinion those endings contain a little more ingenuity than the ending to "Prescription: Murder." Not only is "Prescription"'s ending unconvincing, there is also nothing about it that is particularly clever.

The spoiled wine setup and the notion that Ken had to rely on his partner's talents even in order to murder him are somewhat clever and interesting. Simply getting an accomplice to talk is not clever or interesting.

I recently re-watched Prescription: Murder and, of course, the weakest thing about it is indeed that Ray falls into a trap that a little kid should have seen coming. Another thing I noticed was that the sequence where Ray messes up the apartment to make the crime look like a burglary just seems to go on and on. Compare that with the similar bit in Murder by the Book, where we get the idea in a few seconds. Or any of the other phony break-ins that got staged over the years, for that matter. I did like the music that played while Ray was doing the dirty work, though. And, for being the first Columbo, P:M will always have a special place in the canon.