This book was first published in 1958, so it was already out of date when I read it as a kid. I never noticed. This was one of my favorite books when I was about ten. Recently I picked up a used copy and reread it, half dreading what I might find.
Fortunately, it's held up so well that with a few exceptions, it might as well have been written last year. Henry Reed is the son of a diplomat living in Naples; he's thirteen and has just arrived in the states to visit his aunt and uncle for the summer. They live in a tiny town near Princeton, New Jersey. It turns out that the only kid in town even close to his age is a twelve-year-old girl named Margaret Glass, who goes by Midge. With Midge's help, Henry sets up a research business in a barn to see if he can make money over the summer.
I'd most dreaded finding sexism that I didn't catch as a kid, but I was pleasantly surprised. Henry is never disparaging of Midge because she's a girl, only because she's younger than him and has a sense of humor he doesn't appreciate. She's not a girly-girl, either. The two of them have fun but realistic adventures, from trying (repeatedly) to capture Midge's escaped pet rabbit to rigging up their own weather balloon. The story is funny, the characters all likable, and the sensibilities surprisingly modern. I'm glad I reread it. Now I need to dig up the sequels.