Plot summary from the excellent Whippit Inn - the premier Carry On site (See links)
India, 1895. In the North-West Frontier Province, an atmosphere of calm pervades. For the Governor, Sir Sidney Ruff-Diamond, the most important thing is that the British should beat the Indians - at polo. He and his wife, Lady Joan, are attending a match against the local side, the Kalabar Rovers.
Also at the match are Rhandi Lal, the Khasi of Kalabar, and his beautiful daughter Princess Jelhi. The Governor and the Khasi smile graciously at each other, but behind the Indian Rajah’s smile lies a fervent desire to be rid of the British. Rebellion is always on his mind but he knows that so long as the famous Highland Regiment, the Third Foot and Mouth, is present, victory is out of the question.
The fearless Scottish Regiment strikes terror into the hearts of the natives, who refer to them as the Devils in Skirts. But the regiment’s hard-won reputation is about to be lost, as the result of one man....
At the famous Khyber Pass, a soldier of the Third Foot and Mouth is doing extra Guard duty. He is Private Widdle, who wears a hot water bottle in his sporran. Two Indians approach and try to persuade Widdle to let them through. One of them Bungdit Din, pulls out his scimitar and offers it as a bribe. Widdle takes one look at the flashing blade - and faints. With natural curiosity, Bungdit Din raises the hem of Widdles kilt, and an awful secret is revealed....
The Khasi is overjoyed. Here is his chance to discredit the Devils in Skirts and throw the British out of India! Sir Sidney Ruff-Diamond, however, is most upset - this could mean the end of his cushy job as Governor. He goes to see the Khasi, taking with him Captain Keene and Sergeant-Major MacNutt.
Sir Sidney explains that the whole affair was a terrible mistake. The Khasi asks for proof and Keene and MacNutt are ordered to raise their kilts. They refuse. For they, like Widdle, are wearing drawers, and to the Khasis delight, all is concealed where it should be revealed. The Third Foot and Mouths reputation is in tatters.
Back at the residency, Sir Sidney orders a surprise inspection of his troops. Much to his horror, they are ALL wearing drawers. Worse, Lady Joan secretly takes a photograph of the display. She has taken a strong fancy to the Khasi, and thinks that if she gives him what he wants, he will give her what she wants.
She takes the photo to the Khasi, who is delighted. Show this to the Burpa tribesmen, and they will have no fear off attacking the British, he thinks. But Lady Joan will only let him have the picture on one condition, which doesn't appeal to him, claiming that he has servants to do everything for him, including making love. Her Ladyship decides to wait for him to change his mind.
Princess Jelhi is a witness to Lady Joan’s betrayal. She hurries with the news to Captain Keene. Although they have only met once, the couple are in love, and fearing for his safety, she tells him to leave India immediately, before the uprising.
Keene reports it to Sir Sidney. The photo must be recovered before the Khasi can show it to the Tribesman. Keene and MacNutt volunteer to try to get it back. Private Widdle is told that he has 'volunteered' as well, and so is Brother Belcher, a missionary with an eye for the ladies.
Disguised as Burpas, the fearless four infiltrate the Burpa tribesmen just in time to hear the Khasi inciting them to revolt. Keene is relieved to learn that the Khasi hasn't yet got the photo, and that, as yet, the Burpas are unwilling to fight.
Trying to break into the Burpa stronghold, the four find themselves in a roomful of beautiful girls, all generous with their charms. In the 'passionate' moments that follow, all four men fall in an ornamental fountain. This washes the disguise from their faces and they are captured.
They are sentenced to death, and so is Lady Joan. Hearing of this, Jelhi goes to the rescue. She and Joan go into the prison, and, with the aid of a couple of most un-ladylike right-handers from her Ladyship, they knock out the guard and free the men, who disguise themselves as nautch dancers.
Unfortunately, Bungdit Din, who, mistaking them for real dancers, orders them to perform before the Khasi, spots them. Their attempts are chaotic. But in the confusion they manage to escape.
With the help of a fakir, the six get over the wall of the Burp Stronghold and return to the residency. They are followed by the Khasi, who gives Sir Sidney an ultimatum: the British must leave India at once, or be wiped out by the Burpas.
Faced with this dastardly threat, Sir Sid shows the Khasi that the British are made of stern stuff. He tells Major Shorthouse to order the residency staff to join him for dinner - black tie of course.
The Burpas launch a fierce attack, and while all about them are losing their heads, the residency residents keep theirs and enjoy their meal.
Eventually, when the building has almost been razed to the ground, Sir Sidney takes action. He walks into the middle of the battle, orders what's left of his men to line up facing the enemy and its 'Up kilts, and at 'em.'
The Burpas take one look - and flee in horror. The Third Foot and Mouth have lost their drawers - and regained their reputation. The British Raj is safe once more!