Granny buys a horse and buggy for Mrs. Drysdale so that they can have buggy races, but she gets her an old broken-down mare and names it Lightnin'. Jed tries to teach Granny a lesson by switching horses with Granny's champion harness racer, Ladybelle. Mrs. Drysdale agrees to race when Mr. Drysdale promises her that the Clampetts will leave Beverly Hills if she wins. Granny uses her tonic to put some life back into Lightnin' before the race.
—efmartin