From 1987: the most insane season ending cliffhanger in the history of US Primetime soaps (forget the Moldavian Massacre): Fallon Carrington Colby is kidnapped by a passing UFO (really!) in the season two finale of THE COLBYS (aka DYNASTY II: THE COLBYS).
There was no season three.
However, the storyline was wrapped up in the eighth season of DYNASTY, the show that spawned this ill-fated spin-off, when Emma Samms rejoined the original series.
The effects work is pretty impressive for a show that everyone involved must have suspected was terminal (why else would you pull a stunt like this?) and, contrary to popular belief, the miniature work isn't recycled from similar disco-equippped alien craft in CLOSE ENCOUNTERS OF THE THIRD KIND (of course), GALACTICA 1980 or THE GREATEST AMERICAN HERO.
Fallon had originally been played by Pamela Sue Martin (THE HARDY BOYS AND NANCY DREW MYSTERIES) but she bailed at the end of Dynasty's fourth season, only for Samms to step into the role (without explanation, naturally) the following season.
Keep watching the end credits for a bevy of Star Age stars drafted in to bolster the spin-offs flagging ratings.