This is a very, very vague question, so do bear with me.
Long years ago I had a children’s book about a bunch of kids who get into adventures and suchlike. The author was not Enid Blyton, and I can’t remember who it was. There was this particular story about some caves. The children go spelunking and discover some fish that have evolved without optical apparatus owing to how the cave is perptually dark. The fish are valuable as they can be sold to a museum for pots of cash which were required to fund some activity I have now forgotten. Obviously, there was the necessary villain who provided excitement in everybody’s life. Hijinks ensued, the goodies won, and the baddies hung their heads in shame and/or were sent to jail.
Now about my question.
One of the teenage female protagonists was a member of this society that existed to provide support to people. It may have been a charitable organisation (because IIRC there was some amount of knitting involved), it may have been a nursing jig, or it may have been a church offshoot. I don’t know.
Please help me figure out what this society was. One starting point is that there was a “Four” in its name, and an alphabet. So “Four F”, “Four D”…do any of these ring a bell? Any information would be welcome.
Also, any information about the book and its author would be welcome too.