A brand-new young chapter book series from Edgar Award winner Dori Hillestad Butler! When ghost boy Kaz’s haunt is torn down and he is separated from his ghost family, he meets a real girl named Claire, who lives above the town library with her parents and her grandmother. Claire has a special ability to see ghosts when other humans cannot and she and Kaz quickly form a friendship. The two join forces to solve the mystery of the ghost that’s haunting the library. Could it be one of Kaz’s lost family members?

After successfully solving the mystery of the ghost in the library, Kaz and Claire land the first case for their detective agency—a haunted attic in a neighbor's home! With a little help from Grannie, Kaz and Claire discover that what appeared to be something spooky has a much simpler explanation.

Kaz and Claire’s new detective agency is a success! Their latest case, though, is proving to be the hardest yet. When Claire’s classmate says he saw a ghost backstage while rehearsing the school play, Kaz goes to school with Claire to investigate. From the description the boy gave, Kaz is sure it’s his mom—but where has she gone? Kaz and Claire search everywhere and find no trace of her, but the mysterious ghostly activities are still happening…

Kaz and Claire are called in for another ghostly mystery, and this ghost is always right on time. When Claire's friend tells the young detectives about his five o'clock ghost, Kaz wonders if it could be his own missing brother, Little John. Kaz and Claire search the house up and down, but they can't find any trace of Little John—or any other ghost. Yet when five o'clock comes along, the strange occurrences come back again...

Now that Kaz can finally pass through walls without feeling all “skizzy,” he can go explore Beckett’s secret room at the back of the library. What he finds there is a mystery he never expected!

With a lot of searching and a lot of luck, Kaz has found his dog Cosmo, his little brother Little John, his grandmom, and his grandpops. But what about his parents? Or his big brother Finn? Will he ever see them again? Kaz wants to keep looking for his family, but when Claire hears about a ghost at the fire station, Kaz knows it’s a case for C & K Ghost Detectives!

A group of girls in Claire’s town have noticed strange sights and sounds coming from the tree house where their club meets. Is it a rival boys’ club trying to scare them away? Or is it a ghost? The girls ask Claire to tackle the mystery—and Kaz hopes to finally find the rest of his missing family members! From the Trade Paperback edition.

Kaz are Claire are called on for another case! A family thinks their house is haunted, making it difficult for them to sell it. Will Kaz and Claire be able to figure out what's going on, and find more of Kaz's family members along the way?

Kaz are Claire are on the case again—this time, they're looking for Kaz's long-lost uncle! Their search takes them to a bakery and a movie theater. Along the way, they meet another kid ghost detective. Will Kaz and Claire be able to figure out what's going on?

It's almost Halloween, and Kaz and Claire are off to Seattle to visit Claire's cousins. They explore the local library...and find a ghost living there! The ghost's family has been missing, so Kaz and Claire decide to investigate. When they discover ghostly activity in the city's subterranean passages, they put their detective skills to work. Kaz and Claire are on the case!"