Well, I was a bit wary of this week's "Once Upon a Crime," since it seemed like doing a fairy-tale murder episode was turning the show into a commercial for another (inexplicably) successful show on the same network. But it turned out to be a fairly solid mystery that didn't require as much suspension of disbelief as a lot of their recent stuff. It even had the clincher clue be a classic type of mystery-story clue, a detail of how the victims were dressed. Nothing I haven't seen repeatedly before, but sometimes it's nice to see the classics revisited.
I'm disappointed in myself, though, because I almost cracked the case very early on. As soon as they found the third victim in the pattern still alive, my first thought was "She's the killer and only pretended to be attacked to throw off suspicion." But I dismissed the idea because I couldn't think how she could've timed her dose of the drugs to ensure she'd survive long enough for the cops to get there. It didn't occur to me that she was watching and took them just as the cops drove up. (Although it was kind of cheating to reveal at the end that she'd received a nonfatal dose; you'd think that would've come up earlier in the investigation and made them suspect her.)
Martha's excuses for turning Castle's apartment into her workspace and performance venue felt a little contrived; it was easy to see that the writers were stuck with using the standing sets and trying to rationalize it. But then, that's a perennial problem in TV and has been for decades, because building new sets is expensive.