If you liked the 39 Clues series,
try these read-a-likes.

Chasing Vermeer, The Calder Game and The Write 3
Blue Balliett

Calder, Petra & Tommy solve mysteries deep in the art world.  Paintings, sculptures and friends ships are put to the test.

Roman Mysteries
Caroline Lawrence

In Rome in the year 79 A.D., a group of children from very different backgrounds work together to solve mysteries

Holes
Louis Sachar

As further evidence of his family's bad fortune, Stanley Yelnats is sent to a terrible correctional camp in the Texas desert.

Secret series
Pseudonymous Bosch

Two 11-year-old misfits try to solve a mystery and stop the evil Dr. L who is searching for the secret of immortality.

The Jaguar Stones trilogy
Jon Voelkel

When Max discovers his parents have disappeared while excavating an ancient Mayan site, he sets off in search of them

The Sherlock Files series
Tracy Barrett

Xena and Xander Holmes discover that Sherlock Holmes was their great-great-great grandfather...

Kari & Lucas Mysteries
Susan Runholt

14-year-old best friends Kari and Lucas solve international mysteries in the art and music worlds.

Skeleton Creek series
Patrick Carman

Although housebound, Ryan continues to investigate the strange occurences in his hometown of Skeleton Creek

Missing series
Margaret Peterson Haddix

13-year-olds Jonah and Chip learn they were discovered on a plane that appeared out of nowhere, full of babies with no adults.

Something Wickedly Weird series
Chris Mould

11-year-old Stanley discovers that along with a house, he has inherited a host of mysteries surrounding his great-uncle's death.

The Oracles of Delphi Keep
Victoria Laurie

3 orphans find a magical portal in their quest to locate six silver boxes before the evil Demogorgon's offspring.

Theodosia series
Robin L. LaFevers

11-year-old Theo uses knowledge and special talent to protect the world from ancient Egyptian magic that has fallen into the wrong hands.

Peter and the Starcatchers series
Dave Barry

Peter sets sail on the ship Never Land and befriends a young Starcatcher, whose mission is to guard a trunk of magical stardust.

Ulysses Moore series
Pierdomenico Baccalario

11-year-old twins Jason and Julia discover twisting tunnels, strange artifacts, and a mysterious, locked door in their new home.