On a cross-country vacation with their parents, twins Coke and Pepsi, soon to be thirteen, fend off strange assassins as they try to come to terms with their being part of a top-secret government organization known as The Genius Files.

The magic tree house carries Jack and Annie to 1938 New York City on a mission to rescue the last unicorn.

Jack and Annie travel 500 years back in time to Florence, Italy, and spend a day helping Leonardo da Vinci in the hope of learning another secret of happiness.

Witnessing the harrowing events of the Civil War from the sidelines, eleven-year-old Henry endures the most grueling challenges of his life throughout a hot July week when he becomes inadvertently involved in the historic battle.