When FBI Special Agent Carlson accidentally texts a fifth grader to let him know he was kidnapped, he had no idea of his mistake. And most fifth graders wouldn’t know what to do with such a text. But Jordan Waters, with the help of his friends Justin, Stephanie, and Catherine. was no typical fifth-grader. They were The Math Kids, and they had helped the FBI before, using math to help solve the kidnapping of Catherine’s father and a cold-case bank robbery.

But this was different. Agent Carlson had been kidnapped, and they didn’t know any other FBI agents. They tried calling the agency, but there were too many agents for them to find the person they needed. Until some quick thinking by Justin, who realized that the agent’s last name was probably similar to his friend’s name, and that gave them the name of an agent would could help them, and more importantly, help Special Agent Carlson.

It’s not until they knew their FBI friend was safe that they found out what had happened—he had been doing research on a case in Cairo, Egypt, when he’s been captured. He was able to get away, but he was no closer to solving his case. A billionaire had gone missing. He was presumed dead, and if no one was able to figure out the riddles in his will, then all his money would go to his lawyer. The FBI agents knew that there was something strange going on, but they couldn’t figure out the riddles.

The will mentioned “the great triangle,” and Agent Carlson took that to mean the Great Pyramid, so he had gone to Egypt. But Catherine had been studying triangles, and she thought that the agent was on the wrong track. Her father had taught her a little about Blaise Pascal and the triangle he came up with that is full of patterns. She thinks that is the great triangle that the will referred to, and she thinks that the riddles will be solved by using Pascal’s triangle.

But they are up against a deadline. The Math Kids only have so much time to solve the riddles before the lawyer gets all the money. And when Agent Carlson’s kidnappers show up back here in D.C., they all realize just how dangerous this puzzle is, and how important it is that the good guys find the answers to the riddles first.

The Triangle Secret is the sixth in The Math Kids series, and this may be their biggest case yet. Author David Cole combines his years of mathematical learning and his years of teaching children into these books that use math puzzles to solve crimes. These kids are smart and honorable, and these stories show how math can come in handy in real life. There is even some extra information at the end of the book, about the abstract artist Catherine had been studying, about Beethoven, and about other unusual wills.

I enjoyed this book. This is the kind of book I would have loved as a (nerdy) kid. I would have found the puzzles really interesting (similar to Encyclopedia Brown, but with lots more math). But what I could have really enjoyed is reading about the friendships that these friends have built. They support each other, no matter what pastimes they’re pursuing, and they work together to find the answers. I don’t think these books are for any kid, but I think smart kids who are curious about the world and interested in finding answers to their questions and solving puzzles will find some friends with The Math Kids.

Egalleys for The Math Kids The Triangle Secret were provided by Common Deer Press through NetGalley, with many thanks.