John Williams must have appeared in more episodes of "Alfred Hitchcock Presents" than nearly everyone...except for Alfred's daughter, Patricia. So, seeing Williams in an episode only a few after he starred in three straight isn't all that surprising.
In "The Three Dreams of Mr. Findlater", he plays Ernest Findlater, a mousy and rather dull man with a penchant for retreating into a dreamworld instead of interacting with his cold wife. In this dreamworld, Ernest dreams of a Polynesian girl, Lalage, and a nice tropical island. But she also appears to him at other times and they dream of being together and killing his wife. However, because Ernest is so mousy and timid, he always dreams and plans...but never actually does anything.
There is no twist, no coincidence, no 'Hitchcockian' moment in this one....just the man dreaming of being with his imaginary girlfriend and killing the wife....and nothing more. Interesting to watch but ultimately disappointing.