This was an oddball episode, trying to take advantage of the disco popularity, which by the time this episode aired in 1979, was 2 years past the disco peak.
A lot of the disco scenes take place during the day, which admittedly is kind of silly. The string of murders committed only appears to be tangently related to the actual disco, all of the older victims were killed somewhat close to the location but not in or around the disco itself.
The Angels guess that the murderer might be one of the patrons or someone who works there, but that's all it was, a guess, and a lucky one at that.
The cast is okay. Peter McLean plays Fred Heston the owner of Freddy's Disco. He's having an affair with Shera Danese's Connie who works at the establishment. McLean also played in first season episode "I Will be Remembered" as Frank Ross, the sketchy, conniving agent to Ida Lupino.
Diane McBain places his wife, who wanders around the bar area angry most of the time. Zalman King does a whack and over the top turn as Harry Owens, the house DJ, who from the opening scene is apparently mentally unstable. There's a few other supporting players but they're hardly worth mentioning.
Kris goes undercover as a disco instructor and she has scenes with a young male dancer. Kelly goes undercover as someone working for a record company (and the issue of payola briefly comes up), most of her scenes are with Zalman King, who naturally hits on her, but Kelly ain't falling for him. Sabrina goes undercover as, what else, a magazine writer, who says she wants to do a big story on Freddy's Disco.
The plot is bare bones and mostly about setting up the characters. There simply isn't really much going on here beyond what I just described which leaves very little for the Angels to do until the killer strikes again. Which he does.... in broad daylight, awkwardly stalking someone.
Nothing great here, just a setting without much plot driving it.