Then
By book 104 I had been reading BSC for years and knew everyone in Stoneybrook like they were real people. Abby was the newer addition — she and Anna showed up in the nineties when the series was reinventing itself — and I liked her because she was loud in a way the earlier members weren’t. This one being about her twin felt like getting a whole new character for free.
I also had a thing about twins. I wanted to be one.
Now
The late-era BSC books get a bad reputation and some of it is fair — by the hundreds they were written by ghostwriters following a tight formula — but Abby’s Twin still does something the series always did well: it takes a kid’s internal experience seriously. Anna’s conflict about her violin and what she actually wants versus what she’s been building toward is a real conflict. It doesn’t get dismissed as a phase.
A hundred and four books in and Ann Martin’s world still had room for a story like that. That’s not nothing.