The short begins with a live-action introduction of Calloway and his orchestra, who perform a short chorus of "Minnie the Moocher" (Calloway-Gaskill-Mills) before performing a vamp of the title song, "The Old Man of the Mountain" (Young-Hill (Brown)).
As the cartoon proper begins, a lion on roller skates (made of rabbits) rushes from his guard post atop a mountain, racing into a nearby village shouting "Look out! The Old Man of the Mountain!" The lion's warning sparks a mass exodus of the other animals who pack up their things and start to flee as the lion continues to warn "Look out! The Old Man of the Mountain!"
In time, Betty Boop emerges from a guest house in order to find out what is going on. She confronts a passing owl, who in song describes the Old Man of the Mountain, a predatory hermit who threatens the livelihood of the villagers, particularly the women. Despite the owl's warnings, Betty is curious and declares, "I'm going up to see that old man of the mountain", and starts a trek up the mountainside. She passes several people fleeing from the Old Man, including a woman pushing a carriage with her triplets—who look suspiciously like the Old Man of the Mountain.
When Betty gets to the top of the mountain, the Old Man of the Mountain emerges from behind a rock. Over twice as tall as Betty, the Old Man backs the girl into his cave and, as Betty fights off his advances, begins to sing with her a duet of "You Gotta Ho-De-Ho (To Get Along with Me)" (Robinson-Hill (Brown)). Betty loosens up and joins in, and the two begin to flirt with each other. After his first verse, the Old Man looms menacingly over Betty.
"What'cha gonna do now?" Betty asks, frightened.
"Gonna do the best I can," the Old Man replies, launching into a jazzy dance routine. The Old Man and Betty continue to dance together, but when the song is over, the Old Man makes a lustful grab for Betty, who runs for her life back down the mountainside.
The Old Man gives chase, and grabs Betty just long enough to catch hold of her dress, which Betty jumps out of. As Betty finds refuge behind a large tree in her underwear, her dress comes to life and slaps the Old Man before running back to its owner. Betty climbs the tree to apparent safety, but as the Old Man comes over and attempts to coax her down with "The Scat Song" (Calloway-Perkins-Parish), he picks the tree up and bounces it on the ground, causing Betty to slide down.
Before he can have his way with her, however, the animals from the village rally to Betty's aid and surround the Old Man, tying his arms and legs together by a tree. They then proceed to beat him up, tickle and humiliate him, thus exacting revenge for all the times he had made their lives a misery, with Betty watching with glee.
According to film historian Christopher Lehman, the sexually suggestive nature of this film caused "some Americans at the time, especially Catholics," to complain to exhibitors who then pressured Paramount Studios (distributor of the Betty Boop series) to tone down the Betty Boop character, which subsequently pressured Fleischer Studios to do the same thing. This can be seen when an old man sees Betty and acts crazy, a fish starts to follow her before getting hit by his wife, and Betty's dress even is removed in one scene. According to Lehman, "In dispensing with the African-American entertainers and their music after limiting the 'Betty Boop' series' sexual references, [Max] Fleischer thus acknowledged the widely assumed connection between raciness and blackness." After 1934, African-American jazz music (which was, in fact, often racier than other musical forms, though not exclusively so) would no longer appear in Betty Boop cartoons, and she metamorphosized into a more conservative, mature, domestic character who often played only a supporting role.