Apparently, this is only considered minor Curtis but I thought it was pretty well-done for TV. Many films have been made associating femme fatales with the black widow spider, but this gives it a literal spin, thus linking it with the 'atomic monster' cycle of the 1950s where various insects caused widespread panic and terror after growing to enormous size. Ingeniously, this adds yet another level to the mystery (and the fun) by making the villainess a twin (though not identical) so that, once one has swallowed the notion (given incontrovertible evidence in the wake of its killing-spree) that a woman could in fact turn into a monster, there still remains the question of identifying her...and, making the process all the more tougher, is the fact that the lady concerned suffers from schizophrenia and assumes this form (for whatever reason, during the cycle of the full moon) once her other personality takes over!
It seems complicated and it is, with a number of questions remaining unanswered by the end of it: a young girl is eventually established as the daughter (born from a rape!) of the villainess (the twist in the final shot making it more than clear in this case) but she calls both her and her sibling "Aunt" – then who does she think is her mother? Likewise, an old woman is addressed as "Granny" but she is not the twins' mother (played by SHE-WOLF OF London {1946}'s June Lockhart), who is thought to be dead but is actually being held, blinded and crazed after an attack by the monster (about to be victimized again at the climax, she is so distraught as to throw herself out the window!), in a back-room of the house! Confused yet? It transpires that Granny (who goes by the name of Olga and is played by June Allyson, formerly a syrupy lead at MGM) knows about the woman's many afflictions and protects her, while the other twin is completely oblivious to the melodrama going on in their family home! By the way, Donna Mills and Patty Duke Astin appear as the twins, one chic and sought by several men (including those supposedly going out with her sister!), the other somewhat frumpy and introverted.
On the other side of the spectrum, we find down-on-his luck private investigator Anthony Franciosa (I wonder whether his reliable turn here landed him the starring role in Dario Argento's TENEBRE {1982}) who actually almost got it himself in the very first scene and, naturally, he subsequently determines to get to the bottom of things and unravel the mystery. In this, he is helped by his adoring but ditzy secretary (Roz Kelly) and hampered by Police Inspector Vic Morrow (who knows what is going on but does not want it to get around so as not to alarm the community: it was weird watching the actor's uneasiness at each grisly scene-of-the-crime when his own tragic and notorious death 5 years later on the set of TWILIGHT ZONE: THE MOVIE {1983} must not have been a pretty sight either!). The latter's partner (Max Gail), however, proves more receptive to Franciosa's probing, and also involved are "guest stars" Sid Caesar (operating from an office opposite the hero's and constantly complaining of the cold, aggravating Kelly in the process) and Jeff Corey (as the Indian guide who found the twins, still mere toddlers, and their mother when the plane they were on crashed – with the spider bites received by one of the girls resulting in her current predicament).
Anyway, the film is absorbing and very enjoyable along the way, if not without flaws (apart from those already mentioned): for instance, in the last half-hour or so, when Astin takes center-stage with a bravura performance, a lot of things happen (including two transformations!) in the time it takes Franciosa and Kelly to reach the house (I understand it may have been located some distance from the city but, then, cut-aways to the speeding car should have been incorporated because, as it is, one tends to forget that the hero was even on his way there!). The monster is not too badly rendered, even taking care to have it rush headlong into walls in pain and desperation upon being set on fire (established earlier on as the sole method of destroying the beast).
