Stanley is currently furious with his best friend / bowling buddy, Jerry Gordon, and Helen can't stand him while he's in this state. So she secretly talks to Jerry (Art Kassul, "The Black Marble") in the hopes of getting him to patch things up with Stanley. She asks to use the kids' apartment, so *naturally* the kids end up with the wrong impression, that she wants to use the apartment for a fling. Now everybody has to keep Stanley from finding out (he intends to fix the kids' stove), for he's certain to immediately get the wrong impression.
"Helen's Rendezvous" is an absolutely hilarious episode, with all cast members firing on all cylinders. The best moments are the farcical ones, with Helen & Jerry trying mightily to avoid being discovered. (Along those lines, the most devastatingly funny moment for me has Stanley catching a glimpse of Helen peeking out at him from behind the kids' shower curtain!) And Jack has to maneuver Stanley into the girls' bedroom in order to give Jerry some precious seconds in which to escape. It's also hilarious when Jack & Chrissy try to convince Stanley that the "Illicit Fling" is a new dance craze.
There are two interesting takeaways from this story, though: Stanley can't be that good a judge of character if an unscrupulous lech like Jerry is his best friend, and there really is no privacy at the Regal Beagle, where it's always possible to overhear a conversation.
Eight out of 10.