When she and her grandmother return to Franklin, North Carolina, for a Christmas visit, thirteen-year-old Mandie worries about how all the guests will get along with each other and wonders about the appearance of a mysterious package addressed to her.
Mandie, Celia, and Jonathan are visiting Europe and see a strange woman on ship. While visiting a linen mill in Belfast, Mandie saves a little girl trapped inside.
Harry spends an adventurous three weeks at his grandfather's house. Strange things begin to happen, including sounds in the night, mysterious intruders, and the finding of hidden staircase. All this leads to the surprising climax and the finding of a precious gem.
A young boy and girl see lights at night on an offshore island, row out to the island and discover a cave, and eventually, during a storm, solve the question of what is going on out there.
In 1878 in London, Sally and her companions Frederick and Jim try to solve the mystery surrounding the unexpected collapse of a shipping firm and its ties to a sinister corporation called North Star.