In the trenches during the First World War, two foot-soldiers come upon the unconscious figure of an officer. Assuming him to be dead, one of them, Alf, attempts to rob the man, much to the disgust of his comrade, the steadfast James. When they realise that he is alive they carry him to safety, and the officer, the Honourable Teddy Meldrum, tells them that he is forever in their debt.

Nearly ten years later, we find that Meldrum has repaid said debt to James - he is now serving as 'head of the household' to Teddy's brother Lord Meldrum, a factory-owning aristocrat, and his sprawling family. Following the death of a butler, shifty Alf Stokes reappears on the scene too, claiming his side of the deal; he is duly appointed as the new butler, much against the wishes of James, who remembers all too well Alf's criminal tendencies. At the same time, Alf arranges for a new parlour maid, Ivy, to join the staff. Unbeknown to the others, Ivy is really Alf's daughter and is ensconced in the house to (sometimes unwillingly) help her father swindle the Meldrums out of their money.

All this was portrayed in the premiere episode; subsequent programmes depicted Alf's attempts to fulfil his nefarious dreams, and James's stalwart opposition to this unsavoury character. The battle of wills was played out against a background of heated passion, not all of it unrequited. James was desired both upstairs (by Poppy) and downstairs (by Ivy), while the (not so) Honourable Teddy tried desperately to have his way with Ivy, not necessarily because he fancied her but because it was 'the done thing' to do it with parlour maids. Even Meldrum was parking his boots under the bed of the married but promiscuous Lady Shawcross, while the other young female member of the family, Cissy, dressed like a man, spoke like a man, walked like a man and seemed to have the desires of a man - making Perry and Croft's sitcom an unlikely groundbreaker in the recurring portrayal of a lesbian character.

The writers were determined that You Rang, M'Lord? should have a classy air about it, in keeping with its subject and making it look more like the sort of period dramas (especially Upstairs, Downstairs) that it was parodying. To that end, the episodes were 'drama-length' (50 minutes) and the sets, lighting and camerawork were of a quality more normally associated with such productions. Unlike the writers' previous works (Hi-de-Hi!, It Ain't Half Hot Mum etc, featuring many of the cast used here), however, the lead characters were not loveable; in fact, Alf was quite menacing and James was just too snobbish and unbending a character to generate a response from the audience. This combination of production values and darker characterisation seemed to work against the series, and the normally loud and broad humour of such ensemble romps was uncomfortable in the surroundings. While far from a ratings disaster, it nonetheless failed to attract the level of audiences normally reached by Perry and Croft.