The House of Arden
Alas, when I tried to share the Nesbit magic with my own children, it didn't cross the generation gap. Perhaps her humour was too subtle, perhaps the Victorian-era setting was too far from my daughters' world, or maybe I was too eager and tried when they were too young. All my favourites sit on my bookshelf, but they haven't been read for many years.
Then I found The House of Arden in the local op shop. I hadn't read this one, but for fifty cents, it was worth a punt. (I must say that Edith's prolific output did produce a few duds, and I'd been disappointed by Wet Magic and The Magic City.) But The House of Arden, I'm pleased to say, was right up there with her best.
It's a time slip story, in which two children (unfortunately named Edred and Elfrida) travel through their own family history, encountering highwaymen, the Gunpowder Plot and a mysterious South American civilisation among other adventures, as well as a random fellow traveller from their own time (who is a loose end left dangling -- perhaps resolved in the sequel, Harding's Luck). They are searching for treasure, and eventually find it, though not in the form they were expecting.
I'm delighted to add The House of Arden to my collection, and it's reminded me how much fun Nesbit's books can be. She also had a very complicated personal life, (which possibly explains her fascination with absent fathers??) and I've been promised her biography to read (thanks, Kirsty!) I can't wait...