Nancy Clancy Super Sleuth is the first book in a Fancy Nancy spinoff series, aimed towards older readers. It's about 125 pages, with black-and-white illustrations.
Nancy has decided she's a huge fan of Nancy Drew books, and of course, she's talking about the original Nancy Drew series. Nobody ever talks about the modern Nancy Drew series in that context. She starts a detective agency with her friend Bree, and they solve two mysteries.
The first is the mystery of the twins next door. Nancy and Bree spy on the twins, while they're fighting. One twin gets mad and says, "I'm going to tell Nancy what you did!". The mystery is, what did she do? Nancy goes completely off-base for a while and deduces that the twins are building a giant pit to trap detectives, but eventually she figures out that the twin left a huge, dirty fingerprint on her Nancy Drew book. Nancy figures this out, by using a magnifying glass and fingerprinting kit; it was a pretty good chapter of her being clever and hardworking.
The other mystery is at school. Everyone brought a keepsake to school, for a display during parent day. The teacher's marble goes missing, and Nancy is falsely accused to stealing it. She tries to solve the mystery, with the help of some photographs. I won't spoil the ending, but I'd say it's about as good as can be expected. It's possible to solve the mystery before Nancy does, and there's a joke about how in Nancy Drew books, the culprit is always the mean, ugly person. There's also a somewhat grim joke, about Nancy's investigations never getting interrupted by Mom, because her mother is dead.
Overall, I'd say it's an okay book for third graders. There's a lot more to it than the third-grade Nancy Drew books, because it's longer. The story meanders a bit at parts, but the book definitely falls in line with the Fancy Nancy books for younger readers. Mary wants to read the other books in the series now.