This is one of my all time favorites. I have the TZ's on DVD and I watch them periodically, one after another, savoring the moments. Only the TZs can I watch this way.
The acting between Blondell and Demarest is nonpareil, and the TV repairman you may recognize as the voice of Winnie the Pooh (from the 1960s). They are all accomplished actors of course, but much of their body of work pre-dates my movie experience by decades.
In any case, this isn't an episode that jumps out and surprises you with a 'gotcha' ending. Instead, you know where it's more or less going, but it manages to keep you on edge the whole time with plenty of creepiness and claustrophobia in that NY apartment. The dialogue is filled with great noir one-liners "you and your flea bitten floozie.."...
Highly recommended--not for the 'gotcha' as I said, but for a more enjoyable ride, watching a pair of thespians in the twilights of their careers give a fantastic stage-life performance.