Private William 'Old Bill' Busby (Syd Chaplin), was a 30 year pipe smoking veteran of Her Majesty's Service with a walrus mustache. We meet him in the trenches during WWI, trying his best to stay out of the way of bombs and bullets and bide his time as best he can until he can return to calmer environs.
Old Bill's greatest worry was his fellow soldier, a man called Alphie, or "Little Alf" (Jack Ackroyd). Bill and Alphie found themselves in a foxhole together during a particularly intense period of bombing and shooting, which prompted Alphie to say to Bill that they should get out of there. Bill frowns and says to Alphie, "If you knows of a better 'ole, go to it!"
Back in a widened out section of the British trenches, Alphie removes his helmet and shakes it to remove the mud and debris. In the process he accidentally splatters some mud on a photo that Bill had posted on the side of the trench. The photo was of his wife. That upsets Bill considerably and he gives Alphie a tongue lashing.
Bill decides to lighten the mood by singing while Alphie plays a tune on a small instrument he has. Corporal Austin (Edgar Kennedy), comes along and breaks up their little party, admonishing Bill for hollerin' in violation of the maintain quiet order in the trenches. Bill responds that he wasn't hollerin', he was singing through his nose. Austin informs Bill that he will be on fatigue duty for violating the trench rules. After Austin walks away, Bill gets Alphie to take up his instrument again and this time they play and sing very softly, until a nearby explosion causes them to be buried in dirt and debris up to their necks.
Bill and Alphie march with their regiment back to Bouceret, France, receiving a heroes' welcome. However, Bill doesn't do much celebrating, as his fatigue duty involves walking about and picking up trash on the streets. Bill comes into contact with a tough looking, but friendly dog, who drops a wadded up piece of paper at his feet. Bill unfolds the paper and observes a photo of three scantily clad women. He folds it up and puts it in his pocket.
Bill begins to fantasize himself as an officer and he begins barking out orders to the dog, who comes to attention, sits up on his haunches and patiently watches as Bill goes through his motions. There is a formation of army men standing behind Bill and unknown to him, they respond to his barking out orders. They come to attention and begin marching forward, some of them entering a nearby building. It takes a bit of time for the officers in charge of the men to realize that it's Bill whom they are responding to. One of the officers approaches Bill and demands to know who his direct superior is. Bill indicates that it's Corporal Austin, who is standing nearby. The officer dresses down Austin.
Austin orders Bill to carry a large bale of hay to somewhere nearby. After Austin leaves, Bill orders Alphie to put the bale on his back and carry it. Alphie complies.
A British Major named Russett (Charles K. Gerrard), is shown sitting at the Rooster Inn, conversing with the proprieter, Gaspard (Theodore Lorch). Russett passes Gaspard a secret message. Gaspard goes down to the cellar of his business and reads the message: "
Brit ammo trains destroyed. Strike tonight." Gaspard removes a false front to one of the beer casks there in the cellar and reaches inside and pulls out a passenger pigeon. He fastens the note to the bird's leg and releases it through a window.
The next morning, Alphie wakes up and picks up a pitchfork to continue working on the haystack he'd been working on the previous day. As he thrusts the pitchfork into the stack, it connects with something solid and Bill's head suddenly pokes up on the other side. Alphie had accidentally jabbed him in the butt.
Bill had slept through the call to chow, so he had no food to eat. He sees Alphie with some bread, so he takes that. As he often does, after he's mean to Alphie like that, he reconsiders, so he gives Alphie back half of the bread. Bill then spots a couple of boxes nearby, each with a laying hen inside. Bill sees there's an egg under one of the hens, so he starts to reach to get it, but the hen is very protective and pecks at him. After some back and forth jousting, Bill eventually gets the egg and puts it in his pocket.
Bill enters a pub and sits at a table with a young lady named Joan (Doris Hill). He's enjoying visiting with Joan when a cat jumps up on the table and starts lapping cream from a container. Bill shoes the cat away and it runs across the room and walks over the top of the dog that Bill had encountered earlier and hides behind the dog.
Bill suddenly realizes that the egg in his pocket had broken and he gets up and walks outside, shaking his leg as he goes, feeling the contents running down his pantsleg. When Bill reaches into his pocket where he'd put the egg, he extracts a baby chick. Seeing the corporal approaching, Bill quickly puts the chick back in his pocket.
The corporal questions Bill as to whether he knows anything about a recent theft of eggs from local hens, but Bill remains mum.
Bill gives the little chick to Joan, who adds it to a box containing several other chicks. Apparently Bill thinks the chicks need milk to drink, as he goes off to find a milk cow. He takes a couple of rubber gloves and as he fills one with milk, the cow keeps whacking him in the face with her tail. Bill pokes holes in the finger tips of the glove, then sets it aside and begins to fill the second glove. A piglet comes by and grabs the glove that Bill had already filled. When Bill notices and attempts to shoo the piglet away, the little guy grabs the glove and takes off, with Bill in hot pursuit.
The piglet finds a quiet corner to enjoy the milk, but his tail extends through the slats of a wooden wall and a passing rooster spies it and grabs it, thinking it may be a worm. The piglet takes off again and Bill sees it and jumps a fence, catching his leg on the top rail and flipping bodily to the ground. The chase leads to the cellar of the Rooster Inn, where Bill's attention becomes focused on the several casks stored down there. He puts his finger to the tap of one of the casks and tastes it. Liking what he's found, he grabs a nearby mug and prepares to fill it up. First, he must contend with the entire tap coming loose and spraying beer all over the place. Eventually, he is able to take a couple of deep drinks.
Bill approaches a second cask and pulls on the tap. He discovers it's a false front, as it comes loose, revealing a foot square opening. Bill bends to look inside when a bird comes out of the cask, followed by another. Bill looks behind the cask and there's no backing at all. It's an open cask made for housing passenger pigeons. About that time, Bill hears someone coming so he hides inside the cask. Gaspard comes down into the cellar and bends over to reach inside the cask to see if the passenger pigeon he'd sent off with the secret message had returned. He instead discovers Bill. A struggle ensues and Bill causes Gaspard's hand to get caught in a container, trapping him. Bill then calls out for help and Alphie and Corporal Austin come running. Gaspard temporarily escapes, but Bill quickly catches him and ties him up. Major Russett arrives and Austin quickly claims credit for the discovery and capture of Gaspard, ordering Bill back to fatigue duty.
Russett sends Austin to get some guards to take Gaspard away, but after Austin leaves, Russett unties Gaspard. As Gaspard runs to get away, Russett shoots him in the back.
Out on the street, Alphie is busy telling a group of British soldiers how he and Corporal Austin had captured a German spy. Bill is disgusted at Alphie and pushes him into a nearby water trough.
The German command receives the message sent from Austin by passenger pigeon and the commanding general, General von Hinden (Kewpie Morgan), orders the men to be put on alert for a planned attack at Bouceret.
The British soldiers have a big celebration that night, including a production of a show called "Black Beauty," that Bill and Alphie unknowingly have parts in. While waiting backstage, Alphie and Bill take turns messing around with a sword that Corporal Austin's character will be using in his part as a German officer. Bill, of course, is recipient of an accidental jab in the butt from Alphie with that sword.
Bill decides that there's too much clutter there back stage and orders Alphie to clear out some wooden chairs. When Alphie is too slow about it, Bill starts grabbing chairs and stringing them across his arm and back, gathering probably a dozen of them that way, then uses his right arm to lift and carry and full-size piano. It was an unexpected display of strength and energy on the part of Bill.
Bill is ordered to play the rear-end of a horse in the play, with Alphie the front end. Of course, Bill orders Alphie to switch ends with him. A third soldier sews them into the costume. As the show begins, the first two characters to appear are a blacksmith (Tom Kennedy) and his daughter. The daughter is played by a male soldier. Corporal Austin then appears, leading a black horse (Bill and Alphie), approaching the blacksmith and requesting new shoes for the horse. The blacksmith refuses to do the job, referring to the horse as an "Alpine Camel."
The daughter begs her father to shoe the horse so as to avoid trouble. The blacksmith eventually relents and prepares to shoe the horse. The horse proves to be difficult and doesn't cooperate, at one point grabbing a mouthful of the blacksmith's chest hair and pulling it out in a large clump, then kicking the blacksmith into a tub of water. In the course of the struggle, the horse's tail catches fire, and people begin grabbing and throwing buckets of water at it. As the horse jumps around frantically and the buckets of water go flying in all directions, including onto the audience, the entire stage becomes a disaster area. The backgrounds collapse and the stage curtain falls on top of Bill and Alphie in the horse costume.
General von Hinden's men attack Bouceret. Bombs land in the town and hit buildings, including the theater. The Brits don't have enough men and weapons to repel the attack, so they are ordered to retreat. As the British leave and the German troops march in, Bill and Alphie continue to try and extricate themselves from the stage curtain.
Bert Chester (Harold Goodwin), of the British Secret Service, was at the theater. He'd been assigned to investigate and find a rumored German spy. He sees that Major Russett had stayed behind when the rest of the British had evacuated, and then observes Russett meeting with the Germans. However, when the Germans arrive, they take Chester and Joan prisoner.
Two German soldiers notice some movement under the stage curtain and they pull back the curtain to reveal the horse costume, with Bill and Alphie inside. They are frightened and run. When Bill and Alphie struggle to get up and take off, they scare more German soldiers. Eventually, they find their way over to a place where two real horses had been tied up and were standing peacefully as the German soldiers tending them were getting drunk. Bill and Alphie sidle up next to the other horses and begin nuzzling one of the other horses, who doesn't like that.
The drunk Germans decide it's time to go, so they take up the reins of the three horses and stumble off towards the stable. Bill and Alphie try to escape, but get chased down as they can't move very fast. Bill opens up the trap door in the shoulder of the costume and grabs one of the German's flask of liquor. He and Alphie then begin to drink and get sloshed themselves.
Bill's old dog friend comes around and Bill motions to him to untie the halter rope, releasing them, but one of the drunk Germans catches them again. Everyone is stumbling badly now. When the soldiers notice the horse can't walk right, they decide they'd better put it down. One of the men points and shoots his rifle, but his aim is terrible and he misses badly. A struggle ensues and one of the soldiers accidentally pulls the head of the horse costume off. That pretty well freaks out the two Germans.
The dog then jumps inside the suit with Bill and turns around so that his head is sticking out of the front. As they prance around the area like that, with the dog barking, the German soldiers all scatter and run. Back inside a barn, Bill, Alphie and the dog all get out of the costume, just before some German soldiers arrive and shoot into the costume.
General von Hinden (Kewpie Morgan) is informed that the British had been reinforced and were returning to take back the town and that the Germans had been ordered to retreat. They take off.
Bert Chester overhears orders being given for the town and the bridges to be mined and readied for destruction, but he's still locked up and can't do anything about it.
Alphie and Bill have assumed disguises as French locals and are grabbed by a German soldier and told to deliver some food and coffee to General von Hinden and another officer.
As Bill enters the room where the general and the other man sit going over their maps, he seems at a loss as how to proceed with serving the food and coffee. Bert Chester climbs up on a bench in his jail cell and can see over into the room. He gets Bill's attention and motions to him how to go about serving up the items. Bill still doesn't do very good, making a sandwich by placing an 18-inch long sausage between two pieces of bread and giving it to the general. Then he misinterprets the general's saying "nein," to an offer of sugar in his coffee and puts in 9 spoonfuls of sugar. The general evicts Bill from the room.
As Bill walks out, Chester motions to him that he should knock out the guard and free him from the cell. Bill isn't catching on to that idea very well either, and he walks up the stairs, appearing to be leaving, when he runs into Alphie. They both turn and start back down the stairs, when Bill stumbles and falls. He and Alphie get in a tussle, prompting the jail guard to intervene and break it up. Alphie and Bill knock out the guard and toss him into a wicker basket. Alphie puts on the guards uniform and hat and assumes his station. When two other Germans enter and start downstairs, Bill quickly jumps behind the wicker basket, with the top half of his body showing and the unconscious guard's lower legs sticking out. It appears as though Bill is just sitting there calmly.
The guard begins to come to and move his legs, which presents a problem for Bill as he has to quickly move his upper body to make it appear as though they are connected. He eventually removes one of the German's boots and uses it to whack him in the head and render him unconscious again. The two newly arrived Germans observe all this with confusion.
After the Germans leave, Bill and Alphie hand Chester a rifle through the bars of his cell, then take off. Outside, they commandeer a German car and take off. A soldier on a motorcycle with a sidecar pursues. They travel at high speed over bumpy roads and mud puddles before losing control and rolling the car. The motorcycle founders in some mud too. The German soldier rushes up to the car where it appears Bill and Alphie are unconscious or dead, but as he checks, they raise up and disable him. Bill and Alphie then get on the motorcycle and take off again. Some British war planes flying overhead shoot at them, blowing off the side car containing Alphie. Bill keeps going but crashes off a bridge and tumbles into a river. He feigns being knocked out as two Germans planting explosives on the bridge rescue him. They perform vigorous resuscitation on him.
The British Army approach the town and are at risk of being blown up on the bridge just outside town. Bill has been taken the basement of a building where the detonators for the explosives were located, one for the bridge, the other for the town. Bill knocks out one German and ties the other up after a struggle. That kept the bridge from being exploded until the Brits had crossed it safely. But, it did blow when Russett came inside the room and pressed the plunger. Before Russett could push the town plunger, Bill fights him and manages to cut a wire leading to the explosives, thus saving the town.
When Austin arrives in the room, Russett quickly pretends that he'd found the spy Bill trying to blow the bridge and the town, but that he'd stopped him just in time. Bill is arrested, as Austin isn't about to take his word over that of a British officer. Another British officer orders Bill to be taken immediately before a firing squad. Before Bill is led away, he is able to hit and knock down Russett.
Chester arrives on the scene and informs the British leadership that Russett was the real spy. Bill's execution is stayed and General Stein (Tom McGuire) apologizes to him, asking him if there's anything within reason that he might do for him. Bill asks the general if he could be made a sergeant. The general makes it so, upon which Bill approaches Corporal Austin and orders him to pick up something on the ground. When Austin bends over, Bill kicks him squarely in the butt.