These illustrated chapter books are much like Scooby-Doo mysteries: without adult cooperation, three kids and their animal (bat) friend blunder and quake through scary (but not really) mysteries until they eventually unmask the bad guy. Zoinks!
I had a devil of a time figuring out in which order to read this series - I eventually gave up and assumed it didn't matter. Each book makes references to the fact that Echo used to live in the graveyard, a cousin who's an acrobatic flier, and his Mom bat. "Treasure in the Graveyard" is the book that best explains how the bat came to live with the family, but even when I got to that story I mostly I felt like I was missing too much information.
They're breezy, transparent stories full of sorta lame jokes. Perhaps kids will think they're lovely, but I found it a bit tedious. They're targeted at third-graders, essentially, but there's an advanced vocabulary that seems a bit of a stretch.
I'm not planning to add them to our library collection - I think there's better for this reading level.