When thirteen-year-olds Jonah and Chip, who are both adopted, learn they were discovered on a plane that appeared out of nowhere, full of babies with no adults on board, they realize that they have uncovered a mystery involving time travel and two opposing forces, each trying to repair the fabric of time.

Thirteen-year-old Nina is imprisoned by the Population Police, who give her the option of helping them identify illegal "third-born" children, or facing death.

Twelve-year-old twins Nick and Eryn and their robot stepsiblings, Jackson and Ava, try to save humanity from killer robots.

In a future world of false identities, government lies, and death threats, Luke feels drawn to the younger brother of the boy whose name Luke has taken.

In a future where the Population Police enforce the law limiting a family to only two children, Luke has lived all his twelve years in isolation and fear on his family's farm, until another "third" convinces him that the government is wrong.

Time travelers Jonah and Katherine arrive in 1611 to rescue missing child John Hudson, son of the explorer Henry Hudson, but just as the mutiny on the Discovery is supposed to start, Jonah and Katherine's knowledge of history is tested once again, and they fear that more is at stake than just one boy's life. Author's note includes facts about Henry Hudson's explorations.

After returning the missing children from history to their original time periods, thirteen-year-old Jonah must save time itself when aviator Charles Lindbergh mysteriously appears and kidnaps Jonah's sister.

Twelve-year-old Zola, who has a surprising connection to Jessie, discovers that she is stuck in a fake utopian future, and that those around her are counting on her to help them escape.

Many surprises await twelve-year-old Edwy Watanaboneset when the Freds return him to Cursed Town, including that he has siblings in Refuge City who he will join in boarding school.

Jonah, thirteen, and Katherine, eleven, travel through time to 1918 Russia just as Alexei, Anastasia, and the rest of Tsar Nicholas II's family is about to be executed. Author's note includes facts about the Romanov's and the mystery surrounding their deaths.