“I am Isis, greatest goddess of old!” proclaims a statuesque blonde (Cate Brewer) while unfurling her silver cape. That pronouncement kicks off the comic-mythic whodunit “Isis & Vesco Investigate the Curious Death of Dr. Freud.” The hour-long piece by Monique LaForce earns lots of laughs, but it overplays its conceit like the kind of “Saturday Night Live” sketch that should have ended sooner.