While out in the jungle, Professor Porter is captured by anthropomorphic Leopard Men. They bring him back to the lost city of Opar, a hidden ancient city high up in the mountains. There, it is revealed that a figure by the name of La had sent them to capture her a mate. Disappointed, she commands her people to sacrifice the Professor. Before he can be sliced in half by a sun-powered laser, Tarzan and Jane show up to free him. La watches Tarzan fighting her men off from a balcony above and is smitten by the wild man. She then offers them a tour of Opar. During the tour, she tries various attempts to flirt with Tarzan, only to have Jane get in the way. The queen then offers them to spend the night in Opar while she plots of a way to kill Jane. The next day she talks to Jane, making her feel as though she is a burden to Tarzan. La then offers both her and Tarzan and outing in the jungle, knowing only Tarzan could make it and not Jane. Jane tells Tarzan to go ahead while she mopes back to Opar, unknowingly followed by the Leopard Men. Meanwhile, La leads Tarzan up to a waterfall and tries to have a romantic moment with him when the Leopard Men toss Jane over the side of a waterfall back at Opar. Tarzan rushes off to save her, but is too late.
As La tries to act innocent, Tarzan discovers the Leopard Men pushed Jane over the side and attacks. He is pinned down, and La tries to convince Tarzan to join her. He refuses and is then strapped to the sacrifice table himself. La offers him a choice of staying with her or death. A faithful Tarzan chooses death, and the sun laser begins to make its way to cut Tarzan in two. Suddenly, a fire bursts out and La goes to investigate. It is then revealed that Jane is alive. La follows her through Opar, determined to finish her off, when Tarzan arrives and distracts La long enough for Jane to grab La's staff and use it to get herself and her family out of Opar.
As Opar burns down and Tarzan rides off with Jane and the family, La summons rain with her staff and swears revenge against Tarzan and Jane.
Later, La would be overthrown by her Leopard Men, including Kaj, and her staff was taken from her. The Leopard Men then break into Tarzan and Jane's treehouse, kidnapping Jane. While Tarzan pursues them, he runs into a powerless La who is corned by a rogue leopard. He saves her and the two reach a mutual truce in order to free Jane. They succeed and La takes back possession of her staff from the entranced Jane. When Tarzan leaves with Jane she begins to punish all the Leopard Men who rebelled against her, most of all Kaj. Later, Tarzan discovers that Jane was taken so the Leopard Men could make her their new queen and free them from La's oppression. Sneaking into Opar, Jane and Tarzan manage to take the staff away from La, so that Jane can perform the ritual to restore the Leopard Men to their original leopard forms. Jane breaks the staff and La is turned into dust, with Opar falling into ruins with it. As she dies, La threatens to place a curse on Tarzan, Jane and their family.
As Jane, Tarzan, the Leopard Men and the rest of their friends leave, it is revealed that the upper half of the staff has fixed itself and La's sinister laugh can be heard echoing into the ruins of Opar.