Synopsis by Hal Erickson
Devon Ericson guest stars as Jenny Wood, Janet's younger sister. When Jenny pops into the apartment for a visit, Janet (Joyce DeWitt) asks Jack (John Ritter) to take her out. Many, many hours later, Jack somehow ends up in bed with Jenny. It's all quite innocent, of course (this is Three's Company, not Sex and the City) -- but try explaining things to the outraged Janet. (Incidentally, the name of Devon Ericson's character is an inside joke: in the original Three's Company pilot episode, the Janet Wood character was actually named Jenny).