Tonight 50 years ago, CBS aired S04E21 "Good Night, Baby -- Time to Die!"
McGarrett goes to an apartment of a woman (Beth Brickell) who he has to protect from her boyfriend (William Watson). Carol Rhodes conned an older man to marry her and he was subsequently killed, presumably by L.B. Barker, the boyfriend. But Barker has revenge on his mind and has escaped prison to get Carol.
The episode takes place in her apartment almost exclusively. We also watch as Carol becomes unraveled as more time passes. The ultimate twist happens at the end and it's a zinger! Carol was actually responsible for her husband's death and she set up Barker to take the fall.
Mr. Mike has an excellent review here: http://www.fiveohomepage.com/5-0log4.htm#93
This isn't one of my favorites but there are parts I really like about it. For one, the twist. Five-O must have uncovered more evidence in this case because it seems like a lot of work they went through to snag Carol.
Carol has various visions and how they're interspersed throughout the episode is pretty cool. She can picture Barker closing in!
I also enjoy the ending when Carol throws a framed picture to McGarrett! Danno failed on so many levels to keep control of her!
We also discover a bit about McGarrett. He moved to Hawaii in 1959 when it became a state and he took a break for about a year in 1968 (presumably before the start of S01) and took off for Switzerland. He obviously likes the country because this isn't the first of last time he mentions Switzerland.
Happy 50th "Good Night, Baby -- Time To Die!"!!!