Off the coast of Africa, a schooner the Nancy S is floundering in a storm. On board, wild animals escape from their cages. Tom Redmond, his wife and daughter, and the cabin boy Kolu are aboard. Redmond is washed overboard, but the others escape in longboats with the crew. The captain, J. S. Robinson, goes down with his boat after dispatching a message in a bottle which is eventually found.
Fifteen years later, two safaris start out into the jungle, one headed by Bruce Redmond and his henchmen Slade and La Bat, who are searching for a white girl, known as the Lion Goddess of the Basumbo tribe. Redmond believes her to be Joan Redmond, heiress to a large fortune which he will inherit if the girl is proven to be dead. Jungle Jim, heading the other safari, is following Redmond and Slade to avenge the deaths of Red Hallahan and Tyler, an American attorney who hired Red, as well as to find the heiress. Both safaris finally intrude on the region ruled by the Lion Goddess, and Jungle Jim and his men are attacked by the natives. Fearing that the white men are after her lions, the Lion Goddess sends them into the fray, and both Jim and his sidekick Malay Mike are attacked. Jim and one of the lions fall into a deep pit.
Joan calls off her her lion in time to save Jim’s life. He and Malay Mike, his partner, are captured and brought before the White Cobra, an international criminal wanted for murder who fears that Jim is a government agent. Joan sentences Jim to a fight to the death with a tiger for killing one of her lions. Jim manages to kill the beast, thus winning Joan's admiration. She frees Jim and Malay Mike, much to the annoyance of her supposed father, the Cobra. The latter sees to it that their weapons have blank cartridges when they leave. Kolu alerts Joan to this, and together they find Jim to give him loaded bullets. Unfortunately, Redmond and his men appear and Slade wounds Kolu and tries to kill Joan to complete his deal with Redmond. Meanwhile, La Bat and Jim fight and Jim is knocked unconscious and is carried over a waterfall.
As this is going on, an unconscious Jim is in danger from a leopard, but a monkey distracts the beast until Malay Mike is able to revive him. Then the two follow the safari and rescue her by stampeding a herd of elephants. Then they and Joan go to a nearby village.
Meanwhile, the Cobra learns of the battle and fearing that Joan has revealed the truth to Jim secretly orders the chief of the very village in which Jim and Joan are staying to kill them without Joan’s knowledge.
After Joan retires for the night, the chief has Jim and Malay Mike tied up in a hut and is preparing to kill them, but Slade and his men arrive and battle the natives to get Joan. They start a fire, and soon the hut in which Jim and Mike are bound is aflame.
Joan’s Basumbos appear to battle the Redmond safari, but La Bat gets to Joan and threatens to kill her servant Kolu unless she orders her warriors to leave. Joan agrees if La Bat will allow them to take care of Kolu.
As this is going on, an unconscious Jim is in danger from a leopard, but a monkey distracts the beast until Malay Mike is able to revive him. Then the two overtake the safari, stampede a herd of elephants, rescue Joan and return to her village. That night Jim and Malay Mike, unknown to Joan, are tied up by warriors obeying an order from the Cobra and are about to be killed when Redmond and his men attack the village. A fire starts and the hut in which Jim and Mike are tied to a post is afire.
Joan tries to release Jim and Mike from their bonds, but a burning log falls rendering her unconscious, but Jim is able to free himself and the trio escape the hut.
Later, Kolu reveals the truth to Joan and when they see war canoes with the Redmond expedition as prisoners heading for the Cobra’s castle, they follow hoping to capture them.
When Slade informs the Cobra that Joan has perished in the fire, he imprisons him and his partners. Now he and his sister Shanghai Lil have to devise another plan. He has the idea of passing Lil off as Joan’s mother. But they need the documents which Slade has hidden in the jungle.
Lil pretends to side with Slade and releases him and leads him to the Cobra’s arsenal. But Slade isn’t fooled and has La Bat lock her up in their cell while he prepares to destroy the arsenal.
Meanwhile, Joan shows Jim the back entrance to the Cobra’s castle and Jim and Mike go in and run into Slade, Redmond and La Bat. A fight ensues, during which Jim identifies La Bat as Red’s killer. And Redmond fearing the explosion flees. But Slade and La Bat escape just before the powder explodes.
Joan and her faithful servant Kolu hear the explosion and as they dash towards the castle they run into Redmond, who shoots at Joan wounding her. Kolu carries her to a cave and stations her lions around her as a guard. Luckily for Jim and Mike, a huge door under which they had fallen, protected them from the blast. Ultimately, they escape from the castle and look for Joan. Kolu meets them and leads them to Joan's cave by a short cut over a native bridge spanning a chasm. Kolu and Malay Mike get across safely, but as Jim is making the crossing hand over hand, he is seen by his enemies and fired upon. A bullet hits the rope, breaking it and plunging Jim headlong into the chasm.
Malay Mike sees Jim fall into the river and goes to his aid, while Slade and his men look for Joan. She and Kolu take refuge behind a waterfall, while Jim, by a ruse, captures the pursuing Redmond and Slade and two of their men. La Bat breaks for freedom and is killed by a tiger while Slade and Redmond escape. The Cobra recaptures Jim and Mike. From Jim the Cobra learns that Joan is still alive and is relieved, because she alone can control the Basumbos. Jim and Mike are sentenced to face a native firing squad unless they tell him where Joan is. The natives line up and a score of arrows are loosed upon Jungle Jim and Malay Mike.
Joan and Kolu arrive in time to save the doomed men, Kolu using a shield to deflect the arrows. The Cobra’s men again capture Slade and Redmond. He frees them when they promise to find Jim and kill him. Joan learns of the plot and orders her men to kill the Cobra. Just as they storm the castle, there is a sharp earthquake followed by the eruption of a volcano. The Cobra makes the natives believe he controls the forces of nature and instantly becomes their ruler. A short distance in the jungle, Jim and Mike head for the security of a cave, but Slade and Redmond are already there and fire upon them. Fleeing the hail of bullets, Jim and Mike find themselves in the path of a huge landslide.
Jim and Mike reach the protection of a ledge just as the landslide thunders past them. Slade and Redmond, however, think them dead. They meet Joan and tell her the sad news. She is brokenhearted. Redmond urges her to come to New York with him so that together they can claim the inheritance. She agrees. Back in the castle, the Cobra, now the absolute ruler of the Basumbo tribe, orders the death of all white people in the jungle, including Joan. The war drums beat out the message. Jim and Mike overtake Slade and Redmond, and take Joan from them. A few moments later, Joan, Jim and Mike are recognized by a party of lion hunters who rush towards them to carry out the Cobra’s edict.
Kolu manages to get to the war drums in time to pound out the message "Do NOT kill," just as the lion men are about to kill Jim, Joan and Mike. Perplexed, the natives capture the trio and take them to the Cobra. Meanwhile, Slade and Redmond see an airplane crash in the jungle. The owner is Hawkes, a gun runner, and they enlist his aid. Jim and Mike, taken before the Cobra are once again sentenced to death. They escape, however, and hold the Cobra at gunpoint. He knocks the gun from Jim’s hand as Shanghai Lil comes in. She fires at Jim. He staggers and topples out the window.
Jungle Jim’s fall is broken by a balcony and he reaches the ground in safety. He rescues Malay Mike and they go in search of Joan. She has fallen into the hands of Slade and Redmond, who have taken her to Hawkes’ plane. Hawkes tells them that one will have to stay behind as the plane will carry only three. Slade and Redmond shoot it out. During the exchange of fire, Joan escapes and rejoins Jim. They decide to capture the plane. Redmond seeing the bushes shake at their approach, thinks it is a lion and throws a hand grenade he had taken from the plane. It explodes directly over the spot where Jim and Joan are standing.
Joan and Jim drop to the ground and the hand grenades explodes harmlessly over their heads. Redmond seeking to escape them, is killed by a lion. Slade and Hawkes return to the plane only to be captured and tied up by Jim. Slade, however, escapes after knocking out Hawkes. The latter tells Jim he is a government agent on the trail of the Cobra. Slade, knowing Hawkes identity, goes to the Cobra and the two join forces. Jim’s next move is to have Hawkes fly over the castle to distract the natives while he and Malay Mike enter the castle, but they are surprised by the Cobra and some of his men. The Cobra shouts the order to kill and his spearmen bear down upon the two men.
Joan arrives in time and orders the spearmen to halt. They hesitate between her command and the Cobra’s. But Joan wins the upper hand when she threatens them with destruction from the skies, just as Hawkes, flying over the castle, drops a hand grenade on one of the huts. The ruse succeeds, but when Hawkes lands his plane, the Cobra escapes, and being a pilot, he jumps into the airplane and begins to take off. Jim rushes after him and hangs on the tail. Before the Cobra can take off, Jim drags him from the plane and they fight it out. The next day a squad of planes arrive to take the fugitives back to civilization and justice. Joan and Jim leave for America and happiness together, but the Lion Goddess promises to return with the means to ensure the happiness of her people.