We didn't mean to change the past. Now we have to win the war. A stunning 'what if?' story by a bestselling author about two groups of 12-year-olds - one in World War Two, one in the present day.

Henry, Frances and Lukas are neighbours, and they used to be best friends. But in middle school Frances got emo, Lukas went to private school and Henry just felt left behind. When they come together again for the funeral of a pet gerbil, the three ex-friends make a mind-blowing discovery: a radio, buried in Henry's garden, that allows them to talk to another group of three kids in the same town in New Jersey, USA ... in the same backyard ... eighty years in the past.

The kids in 1944 want to know about the future: are there laser guns? Flying cars? Jetpacks, at least? Most of all, they want to know about the outcome of the world war that their dad and brothers are fighting in. Though Henry is cautious - he's seen movies about what happens when you disrupt the fabric of time - soon the present-day kids are sending their new friends on a mission to rescue a doomed sweet shop. What harm could that do? But one change leads to another, and the six friends accidentally change the course of history in the worst way imaginable: the Nazis winning the war. Now it's up to the friends to change it back.

Co-author Ann Brashares is a New York Times bestseller for The Sisterhood of the Travelling Pants, here writing with her fellow children's author and brother Ben for the first time.