Though a lot of Gilbert's nonmusical plays are hobbled by the problems that intermittently become problems even in his musical ones (over-written dialogue, mechanical characters, "topsy-turvy" plot twists), reading his work is fascinating, because he seems to have done so many things before anyone else did. Time and time again you'll find ideas and devices in Gilbert's plays that would be taken up by later writers, especially Wilde and Shaw. They did it better, usually; Gilbert's Engaged is a very good play that is still effective today, but Wilde's The Importance of Being Earnest, so greatly influenced by Gilbert, is, I think, better-written, especially the dialogue, which makes Gilbert's seem rather flat by comparison. Still, Gilbert did it first.
On the evidence of the play Foggerty's Fairy, Gilbert was even a pioneer when it came to science-fiction plot devices. The play deals with Foggerty, a young man who finds himself plagued on his wedding day by Delia Spiff, an elderly woman to whom he once proposed, who is suing him for breach of promise. A good fairy, Rebecca, offers to help him -- but, being a good fairy, she is bound (in one of those legalisms that always pops up in a Gilbert play) not to do anything actively harmful to his ex-girlfriend. What she can do is give Foggerty a way to alter the past so that he never met Delia Spiff. Which is exactly what he does, and the rest of the play deals with Foggerty's life in the "alternate universe" created by the consequences of changing one incident from the past. Of course it turns out that he's actually made things worse.
The whole alternate-universe concept, and a story dealing with the consequences of changing the past, is very common now but was considered extremely novel at the time, as indeed it was. Probably the best dialogue sequence in the play comes when Rebecca explains, in detail, how each event in our lives depends on all kinds of seemingly unrelated incidents, at the same time throwing in a Gilbertian swipe at the stupidity of family and class pride:
REBECCA. Don't be in a hurry. Think what you're about. If you blot Delia Spiff out of your career, you blot out at the same time all the consequences that came of having known her.
FOGGERTY. But, my good girl, that's exactly what I want to do!
REBECCA. Take care. The consequences of an act are often much more numerous and important than people have any idea of. Take your own case: you come of a good family, and you are proud of it.
FOGGERTY. We are the Lancashire Foggertys.
REBECCA. No doubt. You didn't do much towards it, and I don't see what you've got to be proud of; but still, proud you are. Now you would never have been born if your father had never met your mother.
FOGGERTY. I suppose not.
REBECCA. And your father met your mother in this wise. Some thirty-six years ago, as he was walking down Regent Street, his attentions were directed to a sculptor's shop, in which was a remarkable monument to a Colonel Culpepper, who died of a cold caught in going into the Ganges to rescue a favourite dog which had fallen into it. An old schoolfellow passed by, and, touching your father on the shoulder, asked him to dinner. Your father went, and at the dinner met your mother, whom he eventually married. And that's how you came about.
FOGGERTY. I see. If my father hadn't had that invitation to dinner I should never have been born.
REBECCA. No doubt; but your existence is primarily due to a much more remote cause. If your father hadn't loitered opposite the sculptor's shop, his schoolfellow would never have met him. If Colonel Culpepper hadn't died, your father would never have stopped to look at his monument. If Colonel Culpepper's favourite dog had never tumbled into the Ganges, the Colonel would never have caught the cold that led to his death. If that favourite dog's father had never met that favourite dog's mother that favourite dog would never have been born, neither would you. And yet you're proud of your origin!
FOGGERTY. I see. I never looked at it in that light. It's humiliating, for a Lancashire Foggerty.
The play even ends with Foggerty providing the first-ever criticism of the logical problems inherent in all changing-the-past stories:
FOGGERTY. Let's understand one another. When I took the draught all the consequences of my having known Spiff were obliterated.
FOGGERTY. But if I had never known Spiff I should never have got into a difficulty on account of Spiff, and if I had never got into that difficulty I should never have applied to you to get me out of it, and if I had never applied to you to get me out of it you would never have given me that infernal draught, which has been the cause of all the miseries with which I'm threatened.
REBECCA. Dear me, I never thought of that.
FOGGERTY. In point of fact, I've been saddled with consequences from which, according to the terms of my contract, I ought to have been entirely free.
In other words, if the past has been changed by something that happened in the present, and that in turn has changed the present, then how could the past have been changed? It's the kind of argument you might have about a Back to the Future movie -- 100 years before Back to the Future.