Along the way to entertain and amuse Rose with childish, clownish antics, he mimics the look and sounds of submerged hippos and scratching baboons on shore. After another disastrous encounter with rapids, the Queen is damaged and leaking water. They seek anchorage for a while in the still side waters of the river. After diving underwater, Charlie notices a twisted shaft on the rudder and a broken blade on the propeller. Rose suggests that the work will have to be done underwater: "Couldn't you straighten the shaft without taking the boat up on shore?..." During the repair effort, when he swallows alot of water and she volunteers to help free the drive shaft with him, Charlie rudely dismisses her:

Are you cracked? The currents down there are fierce. I don't want a drowned woman on my hands. What will you be thinking of next?

But when he dives down, she appears by his side - underwater - cooperatively helping him to repair the boat. On the bank, they build a forge fanned by makeshift bellows, heat up the damaged shaft, pound it into shape on a stone, and weld a new blade (all techniques suggested earlier by Rose): "I saw a Masai native working once using charcoal on a big hollowed stone - he had a boy to fan the charcoal...We'll have to make a new blade, then. There's lots of iron and stuff that you could use...wouldn't it be better to weld it on?"

After installing the parts, they continue on their way. As they float down the river, Charlie euphorically exclaims to his new sweetheart: "Pinch me, Rosie. Here we are, going down the river like Anthony and Cleopatra on that barge!" He admires her and compliments her bravery with a lasting impression:

I'll never forget the way you looked going over the falls - head up, chin out, hair blowing in the wind - the living picture of a hero-eyne!

In their river adventure, they now enter an uncharted, unknown portion, and are beset by man-eating and poisonous water creatures in an increasingly swampy, slow-moving river. First, they are attacked by a shroud of mosquitos that eat them alive. To protect his loved one, Charlie throws a canvas tarp over Rose to cover her, and then poles the boat away from the shore. They reminisce about their adventure together and imagine a time (after their love has matured in the future) when they will have a family together: "What a time we've had, Rosie. What a time. We'll never lack for stories to tell our grandchildren, will we?"

In the oppressive, humid atmosphere of the jungle, the river narrows and they become stuck in the reedy channel at the river's end. An exhausted Charlie must get into the waist-deep water and pull the boat through the shallow muck and silt to deeper water. He resigns himself: "What I said about having to get out and carry this old boat was meant to be a joke. It don't look like a joke now." When he emerges from the river and climbs back on deck, leeches cling to his body. Half-hysterical, Rosie shrieks at the sight of leeches on his torso and legs - she dusts the parasites with salt and helps pick them off. He shivers and shudders in horror, revulsion, and loathing while they are removed:

If there's anything in the world I hate, it's leeches - oh, the filthy little devils!

Dreading it, he knows he must go back in the swampy water to finish the job - he winces in disgust, and then slowly submerges himself back into the leech-infested waters. Rosie sympathetically joins him, hacking away the thick growth, and nursing him after he has collapsed: "You're the bravest man that ever lived."

They seem beaten, finished, trapped and unable to continue - famished, ill, feverish, and exhausted - at the end of the lives together:

Charlie: We're finished.
Rose: I know it.

With pride, Charlie tells Rose that they have done the impossible: "I'm not one bit sorry I came. What I mean is, it was worth it." Exhausted and resigned to die, they lie down in the bottom of the grounded boat ready to fall asleep as lovers. At the end of the tropical delta's maze, Rose eloquently prays for mercy:

Dear Lord, we've come to the end of our journey. In a little while, we will stand before You. I pray for You to be merciful. Judge us not for our weakness but for our love, and open the doors of heaven for Charlie and me.

(In a marvelous crane shot different from their own perspective, the camera rises and pans away to show that they are, ironically, only a hundred yards away from the goal of their journey down the Ulanga River - the lake.)

During the night, clouds form and thunder rumbles. Large raindrops splat on white lilies and the storm quickly expands into a deluge (falling on jungle rivers, pink flamingoes, ducks, giraffes, hippos, lions, and a herd of bounding antelope). The drenching rain and windstorm raises the level of the foamy river, breaking down trees and carrying them along in its path. The rising current of water pushes the mired Queen free from her swampy grave onto the lake. They awaken and joyfully view the lake. They take in the African air, with different perspectives. Rose exclaims: "This air! Isn't it wonderful?" Charlie replies: "Yeah, it's like - I know you don't approve, but it's like a shot of gin. It makes your blood race, your face numb and your spirits soar." Rose apologizes for pouring his gin out.

And then they both see the enemy ship, the German steamship Louisa, on the horizon, headed straight for them. They make a run for it back into the camouflaging reeds. With restored optimism, Charlie fashions some makeshift homemade torpedoes with detonators and inserts them through holes in the prow of the Queen, with the object of ramming the German warship. They clean up the boat prior to blowing up the Louisa:

She ought to look her best, representing as she does the Royal Navy.

They argue together about whether their attack mission is a one- or two-person job. Rose insists on going together, but Charlie wants her to wait for him on the east shore - they experience their "first quarrel" together:

Rose: Who do you think you are ordering me about?
Charlie: I'm the captain that's who! And I'm ain't taking you along. You'd only be in my way.
Rose: I suppose I was in your way going down the rapids. Then what you said to me back there on the river was a lie about how you never could have done it alone and how you lost your heart and everything. You liar! Oh, Charlie, we're having our first quarrel.

Charlie agrees that they will blow up the ship together: "All right. It'll be you at the tiller and me at the engine, just like it was from the start."

The intrepid two head for the gunboat to ram it under cover of darkness in an attempted night attack. But a raging storm arises and overturns and sinks their boat in the choppy water, and they become separated. Charlie is picked up by the German warship at dawn, and immediately brought to trial for being a spy. The German captain (Peter Bull) is exasperated and irritated with Charlie for lying and sentences him to death by hanging on the yardarm as a British spy:

The court sentences you to death by hanging. Sentence to be carried out immediately.

Just then, Rose is also brought on board as a prisoner (with a life preserver labeled African Queen), and they are overjoyed to see each other. For a moment, Charlie disavows knowing Rose and further aggravates the Captain who threatens: "I shall hang you twice, I think." When Rose is asked the same questions that Charlie has already lied about, she decides to tell them the truth. The Germans learn of their plans to sink the Louisa with homemade torpedoes: "We came here to sink this ship...with torpedoes." She looks on with pride as Charlie tells how he made the torpedoes. The captain asks how they got onto the lake. The captain thinks their journey down the unnavigable river was impossible, but Rose responds: "Nevertheless."

(Spliced within scenes of their questioning and preparations for their execution are views of the capsized Queen slowly surfacing upside down in the lake, with the torpedoes angled upward above the waterline and aimed directly in the path of the Louisa.)

They are brought on the deck for the hanging. Rose decides to die with Charlie and makes a sentimental request of the captain: "Would you hang us together, please?" The German captain grants Charlie's touching last request - that they be married before the execution (Rose concurs: "What a lovely idea!"). The captain officiates, but leaves them little time to exchange vows and smiles:

Captain: What kind of craziness is this?
Charlie: Aw come on, Captain, it'll only take a minute, and it'll mean such a lot to the lady.
Captain: Very well, if you wish it absolutely. What are the names again?
Charlie: Charles.
Rose: Rosie. Rose.
Captain: Do you, Charles, take this woman to be your lawful wedded wife?
Charlie: (nodding) Yes, sir.
Captain: Do you, Rose, take this man to be your lawful wedded husband?
Rose: I do.
Captain: By the authority vested in me by Kaiser Wilhelm II, I pronounce you man and wife. Proceed with the execution. (The newly-wed couple kiss.)

Just before they are hung, and the nooses are tightened around their necks, an explosion disrupts their post-nuptial execution. The Louisa collides with their partly submerged Queen with their homemade torpedoes on its prow. Among the wreckage of the sinking ship floating in the water, one of the subordinate German officers swims up to the Captain and gives a ludicrous salute.

To their surprise, they are also spared by fate. The newly-married couple find themselves in the water as black smoke engulfs the Louisa. In disbelief as successful saboteurs, they float alive:

Charlie: What happened?
Rose: We did it, Charlie, we did it!
Charlie: But how?

Rose pulls over a piece of the wreckage floating in the water that shows the name African Queen. Charlie is impressed that they have accomplished their goal, and that they are man and wife - although he calls himself "an old married man." He asks his new wife:

Charlie: Well, what do you think...you all right, Mrs. Allnut?
Rose (thrilled to be alive): Wonderful, simply wonderful. And you, Mr. Allnut?
Charlie: Pretty good, for an old married man.
Rose (asking directions): I'm all twisted around, Charlie. Which way is the east shore?
Charlie (cheerfully assuring): The way we're swimming toward, old girl.

As they joyously begin swimming out of the frame toward a friendly shore, transformed into unlikely heroes, they sing: "There was an old fisherman..." as the music swells up with the happy, but improbable ending. THE END appears above the image of the wavy, bluish surface of the lake.

There were three other endings that were considered, but dropped:

• the rescue of Charlie and Rose by a British warship after their battle against the Louisa
• Rose proposes marriage before the first available British consul
• Charlie remembers a wife left behind over 20 years ago in England