The final episode

The final episode (#96) was called "S.O.S." and aired on March 23, 1974.

The plot: Shirley reunites with an old flame and Danny disapproves.

(You have to remember that in those days, cancelled TV shows just "ended". There was no wrapping up all the narrative threads or completion of story arcs. They just vanished. Also, by the end of the Partridge Family, almost every episode had to revolve around Danny: Keith and Laurie had become "supporting characters".)