With this fourth entry the series seeks to rekindle some of the energy drained after the confusion of the last movie. But Maureen O'Sullivan's problems with the role of Jane creates an oddly effective climax for the movie.
Here's the summary. A plane carrying the Lord and Lady Greystoke (named Lancing oddly) crashes on the remote Mutia Escarpment and all the adults aboard are killed by the crash or by natives who discover the crash. The lone survivor is the young baby son of the Greystokes. He is found by Cheetah and his mates who take him (rather roughly actually) to Tarzan and Jane who end up adopting him naming him "Boy". A few years pass and more Lancings come looking. The old Gaboni attack footage is dusted off again but the safari gets atop the escarpment this time with little trouble. Soon we meet the obligatory white hunter named Sande (Henry Wilcoxin) and the greedy husband and wife Lancings (Morton Lowry and Freida Inescort) as well as the noble Sir Thomas Lancing (Henry Stephenson). They meet the Tarzan clan and pretty quickly figure out that the "son" of the Jane and Tarzan is the heir they need to get hold of a fortune. The greedy couple with Sande plot to trick Jane into getting Boy to them and Sir Thomas is tied up. Jane does but has to betray Tarzan by trapping him in a deep ravine. She and Boy are quickly tipped off by Sir Thomas that evil is afoot but he is killed for his trouble. Almost as quickly another murderous tribe captures the safari and begin the torture deaths of the whole party beginning as usual with the unfortunate bearers. Jane plots to have Boy run through a gap in the wall of their prison but is speared in the back. Boy rescues Tarzan after a dangerous jaunt through the jungle. The evil Lancing is killed just as Tarzan and his elephant shock troops arrive to destroy the village and rescue Sande and the Lancing woman. He quickly sends them away and Jane assumes she must go too, but then swoons as if dead. Tarzan embraces her, but she recovers and the trio rides off into the sunset yet again, a happy family once more.
Apparently O'Sullivan wanted out of the role and the original script had her killed off. But executive pressure changed that situation and so she is suddenly all better. But oddly the shift does add an actual moment of tension in a story which by this time was becoming loaded down with predictability. Boy (Johnny Sheffield) is not a bad addition to the cast as he takes up a lot of the screen time that was once overwhelmed by a mugging Cheetah. I prefer seeing Boy to seeing Cheetah larking through the jungle so it works for me here. But it does make Tarzan and Jane even more domestic than before. This time Jane seems to have added shoes to her clothing, making her less and less the daughter of Eden and more and more a product of civilization once again. The first two movies seemed to be about getting her clothes off and the last two about getting them back on again. Johnny Weissmuller is still physically able to do the part, his age not showing too much. His swimming scenes are especially nice in this one and most the swinging in the trees is repeated from earlier films. Tarzan does behave less like a child in this one, a real problem in the previous movie.
Sadly though the movies are getting more than a bit dull as the patterns begin to repeat. The savagery of ERB's Ape Man is getting more and more difficult to discern among all the calm home life that dominates the Mutia Escarpment.