The first episode produced for the second season (as thus Walter Koenig's first time playing Chekov), "Catspaw" is the 'Halloween' episode of the series, originally being broadcast around Halloween 1967 in the U.S.
It also ranks as one of the least favourite episodes amongst many fans. At first I quite liked it and was willing to give it a chance, but sadly, later on it just became unfocused and messy.
The opening shows promise. The dead crewman being beamed up (that fall he takes off of the transporter and down the step is pretty cool), placing a 'curse' on the Enterprise, is good; and I love the three witches on the planets surface. They were probably the only truly semi-scary thing about the episode.
Unfortunately, things soon descend into a rehashed "powerful alien(s) toying with humans" storyline, already seen in several other episodes, and the plot loses its way, being rather padded and going in circles.
There are a number of 'Halloween' elements – a black cat; a dungeon, complete with skeleton; witches; powerful sorcerers... but they all seem rather thrown in, and don't add up to much.
I also agree with others that – with all due respect to the actress who played her – Sylvia just wasn't attractive or as mesmerising enough to work. They needed someone really seductive and mysterious, but she ends up very unconvincing and rather lets the episode down.
Likewise, we get the obligatory 'romantic' scene between Kirk and Sylvia. It didn't work for me, and the fact that Sylvia had so little spark in the first place made it even worse.
I kind of liked how spell of the castle was broken at the end, and, although corny, liked the little alien things on the ground, that were Korob and Sylvia in their true forms. But it was too little too late for a story that had lost its way.
The story starts of with promise, but the later sections just don't hang together at all. A plot involving black magic had potential (the model of the Enterprise being dangled over the candle flame, making the real Enterprise start to overheat, had a lot of scope), but sadly this one just doesn't do it. Definitely one of the second season's weaker outings.