If you like fast-paced adventure stories with a bit of history and archaeology thrown in, give a 39 Clues read-alike a try.
The Name of this Book is Secret by Psuedonymous Bosch
Two eleven-year-old misfits try to solve the mystery of a dead magician and stop the evil Dr. L and Ms. Mauvais, who are searching for the secret of immortality.
Theodosia and the Serpents of Chaos by R.L. LaFevers
Eleven-year-old Theo uses arcane knowledge and her own special talent when she encounters two secret societies, one sworn to protect the world from ancient Egyptian magic and one planning to harness it to bring chaos to the world, both of which want a valuable artifact stolen from the London museum for which her parents work.
The Golden Hour by Maiya Williams
Thirteen-year-old Rowan and his eleven-year-old sister Nina, still bereft by the death of their mother the year before, experience an unusual adventure through time when they come to stay with their two eccentric great-aunts in a small town on the Maine coast.
The Discovery by Gordon Korman
When four kids on a marine expedition for the summer discover a sunken treasure, it is a race against time, sharks, and each other to bring the goods to shore.