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.

In a society that allows families to have only two children, a group of third-borns tries to save themselves and others like them.

In a society that allows families to have only two children, third child Matthias joins the Population Police to infiltrate their system.

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.

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

Kiandra Watanaboneset reluctantly takes charge when she, her brothers Enu and Edwy, and some young friends are captured by Enforcers and sent to a prison on the planet Zacadi.

It's morning as usual at the Skidmore household, until Charles Lindbergh, the famous historical pilot, appears in their living room. Jonah can hardly believe his eyes, and then Lindbergh grabs Katherine and vanishes again. And that's not all. Chip, Andrea, and all the other children from the plane have disappeared too. And worst of all, Jonah's parents and all the other adults in his town have de-aged into children. Jonah is the only one left, and...

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.

Jonah, Katherine, Chip, and Alex suddenly find themselves in 1483 at the Tower of London, where they discover that Chip and Alex are Prince Edward V and Richard of Shrewsbury, imprisoned by their uncle, King Richard III, but trying to repair history without knowing what is supposed to happen proves challenging. Author's note includes historical facts about the princes and king.

When Jonah and Katherine travel to early 1900s Switzerland and Serbia to return Albert Einstein's daughter, Lieserl, to history, her mother Mileva grasps entirely too much about time travel and has no intention of letting her daughter go.