Headquartered in the historic and mysterious farmhouse known as Barton Manor, nine-year-old Johnny Smith and his younger brothers Matt and Cooper secretly fight crime in Rocklin, California with the help of their adventure-loving grandfather. When the Smith boys accidentally surprise a bumbling grave robber, The Sycamore Detective Agency suddenly has a new case. The Barton family tomb holds more secrets than anyone knew, and the mystery of Great-Great-Grandpa Charlie's gold is now at the top of the list. No one knows for sure if Charlie Barton's fortune in gold even exists. Grandpa Jack thinks it does, and he has a hunch that the thief from the tomb is after it, too. One thing is for sure; the family money can't fall into the wrong hands, and this time, everyone is in on the case. To the Smith boys' dismay, their parents and even Chief Mulligan are working right alongside Grandpa Jack to solve the case. Grandpa and the boys race the clock to uncover the mysteries surrounding Charlie and Pearl Barton's tomb, all the while trying to keep The Sycamore Detective Agency a secret. Will they find the gold before the bad guy does... and before their parents find out they know more than they're letting on?